How do I get my dad's Medicare reinstated?

I so hate these Medicare Advantage plans and how they go about getting new subscribers. I have noticed the newer commercials say Medicare Advantage but they still make it seem that you are missing out of advantages thru Medicare. Straight Medicare never had these advantages to begin with. I cringe every time I see a commercial. They are suppose to cover anything Medicare would, my daughter who runs a unit says No they don't. You have to stay in their network to get the advantages. I am so surprised Medicare doesn't oversee them better.

Yes, he probably switched to a MA during open enrollment. I hope you don't have to wait until the end of this year.

call Medicare. They will be able to tell what your dad changed his plan and if it can be fixed. have his Medicare card and social security number when you call.
the Medicare phone number is 1-800-633-4227

It sounds like perhaps he switched to a Medicare Advantage Plan; they are sort of "all in one" plans of varying quality.

Did he receive new ID cards?

Agree with Glad, call your SS office to check on status. How did you become aware of this change?

Call your local social security office. Was it just the supplemental that he changed? Regular Medicare Parts A and B may still be in place.

Or did he pick up a Medicare Advantage plan?