Is it elder abuse when POA all of sudden, after years of getting a 96 yr. old mother her groceries, refuses to get them for her?

If you are so convinced that your brother and his wife (who are the hands-on caregivers at this point) are abusing mom, financially or otherwise, then maybe your best bet is to go and visit mom.

And I'm not talking about an overnight, where, if mom is experiencing some sort of cognitive decline, she can "showtime" while you are there. I'm talking about maybe a month, live with mom, do her shopping, and her errands and run her around to her doctor appointments and anything else that is going along with the job. Tell your brother and his wife to take some time off and pick up the work that they do. It's really probably the only way to get an honest picture about what is going on with your mom and her health and her needs.

If during that time you can come up with some real proof as to these allegations, then file a criminal complaint against your brother and his wife.

But no one here is going to be able to look into a crystal ball to see if there is indeed elder abuse going on. There are people here who have legitimately seen it, while others have thrown around baseless accusations (usually against a caregiving member of the family) and run away with them, only to find out that the allegations were nonsense. Then there is a rift in the family that really can't be healed, the caregiver wants nothing more to do with the job (and rightfully so after being falsely accused) and it makes the almost impossible job of caregiving just that much more impossible.

But, if you really feel this is a possibility, you believe your brother is abusing mom and is only "in this" for mom's money, then the best way to find that out is first hand.

Good luck.

When I was a kid and an adult I used to go get groceries for my grandmother. She would send me to the store with a list and usually large bills to pay for it. ( two twenties for olives, bread and milk) She would go over the list with me before I would go to the store.... "do you know the brand I want", "only wheat bread with a good date" on and on. I had to get a receipt and drop all the change in the bag. When I get back to her house she would go over everything I bought. It was the same thing..... "I don't know this milk looks like skim but it says 1 percent..... did you switch the label" " Olives went up by 5 cents, you better have gotten all my change" This went on for years. She did this to anyone that bought her groceries.
Inflation is terrible right now and everything has gone up. Encourage your brother to sit down with your mother review the purchases and always have a receipt. Your brother just might be tired of having everything questioned.
If he starts to get home delivery of groceries this might cut some of this down but it won't cut it out completely.
I'm not sure if this abuse.

Your Mom should go to an attorney and check into withdrawing POA from the son. She can get a Fiduciary to act for her.
You may want to consider contacting APS in your area with this story if your Mom is unable to afford to hire someone to shop with her. If Brother has hold of the finances and Mom doesn't want him to have this, there is help for her.
You don't say what your Mom's mental condition is. You are getting your info on the phone from her. Are you able to speak with brother?
You may be down to making a visit. Sorry, but it happens and is what family leave is for!
Sure hope you'll update us.

Lots of good advice from others already. Speaking from my experience on one side of this coin, I would consider that your brother does many things for your mom and is being second guessed and questioned about it. It's already a thankless job and now it's become accusatory. Also I would consider if mom has capacity to understand the checkbook. My mom would often send a check to cousin across the country out of the blue for $2500 no questions asked. Then question me over every reimbursement for her own groceries. Also my sibling didn't at first believe that we needed to buy incontinence products for mom so he questioned me about those purchases several times in the first year or so, too. I'm just saying that these are examples of possibilities to consider, especially if you're not there yourself to see firsthand. Also if your mom needs someone to get her groceries or take to doctor appointments and your brother has been doing so for years, then IMHO the right thing for him to do is to make other arrangements for that, not leave mom hanging. Also IMHO the right thing for you to do is make a visit right away to see firsthand before taking action, and to offer real help or a break for your brother.

POA doesn’t require a person to act it simply gives them the ability to act on the primary’s behalf and at their direction, it is in effect as soon as signed and until either the primary revokes, is no longer competent or within parameters outlined in the POA document as some are given for very specific or short term functions (a closing for instance). Once a primary is deemed no longer competent to make decisions for themselves a DPOA goes into effect if there is one, some POA documents are written up to be both. So first while your brother may have POA for your mom so he can help with the finances if she hasn’t been deemed incompetent and is cognitive enough to pick up on discrepancies she still has full control and can make whatever changes she wants to account access or even his “power”, however remember to consider the possibility that your mom is the one confused and your brother hasn’t actually done anything fiscally wrong he may simply have gotten frustrated in the moment of being constantly questioned. Acting as POA and taking on all of the financial responsibilities can be a thankless job. Most of us don’t enjoy sitting down to pay our bills, having to wait on hold for various details, making ends meet and mapping out our financial households now imagine adding second entire household without the actual ability to make decisions yourself on the fly. Then being called out and questioned on all of that work and worry. Now I am not suggesting one way or the other that you don’t have cause for concern but before alienating the people who are doing the heavy lifting perhaps think about your approach and what other factors might be at work here.

Elder abuse is often a high bar, too high but that’s a different topic, when it comes to getting officials to take actual action and while I am infuriated at the thought of the person my mom counts on threatening not to provide her food if she doesn’t fall in line too I’m not sure legally it would be considered elder abuse. If your brother were being paid to make sure she has food or legal responsible as her guardian to provide food and actually withholding it, that might be a different story.

Particularly if this is all info or complaints you have gotten from your mother I would urge you to call your brother and ask how things are going, is Mom getting more difficult? Is there anything you can do from where you are to take some of the burden off he and his wife? Let the conversation ease into what mom told you without being accusatory but rather assumptive that either she is confused or telling tales, took something more seriously that it was meant and you saw that a sign that maybe things are harder on them than you realized. It may be time to think about help in some form for the three of them and you may be met with some resistance from brother and SIL. Don’t immediately take this as a further indication something nefarious is going on, again while it may mean that it may just as legitimately mean they are in over their heads. They have been doing these things for her for a long time based on your post and it can be very hard to admit to yourself never mind other that it has become too much and you can’t do what you think you always have. The truth of it is when caring for an aging parent, even one without a multitude of issues, things get added to the list little by little and you just don’t realize how much more you are doing now than in the beginning when it was a simple grocery delivery each week. Its also easy to feel that you have somehow failed if that loved one you have cared for needs to go into a residential facility or get aids in the home without an ER visit and some medical issue that helps require it but the truth is life is ever changing and stress can creep up without us seeing it coming, there should be no shame in knowing you need help.

Then again it’s always smart to be on guard, keep an eye out for red flags but assume you all want what’s best for Mom.

The short answer is maybe. If it is true that no groceries are being bought, and no doctor visits are taking place, and your brother and his wife have been taking on these responsibilities, and your mother isn't capable of handling them on her own or finding someone else to step in, then yes. If they are only threatening, then no. However, if they are actually stealing from her, then yes again. I think you should find the office of adult protective services in your mother's county or location and ask them to check in on her. Be aware that many times elderly people with dementia believe someone is stealing from them when it isn't true. That doesn't mean it's never true, though. If you can arrange a personal visit to check this out, then that's the best course of action. If not, adult protective services are the next best thing.

If mom is questioning bank entries is she cognizant enough to know if there is something amiss? If so why does she have a POA that is active?

Who is/are the "both" that yell at "her" ? (I am assuming that the "her" is mom)
If your brother does not buy groceries will mom starve? (fine point but HE is not buying groceries. HE is shopping for mom using her money to buy groceries for her.)

And who is telling you that he is not buying groceries? If it is mom is she telling you this can she be believed?
How do you know she is not being taken to the doctor?

You can contact the State Elder Abuse Hotline number and make a complaint.
I think this might require a visit so you can see what is going on.