How do I prove I met ACA health insurance through September, then I went on Medicare, if I didn't receive my 1095 form from the insurer?

[kpike1]

I enrolled in Medicare in October of 2021, but I didn't receive a 1095 form from my previous insurer, for months January thru September 2021

[Cynthiad66]

Did you have health insurance all year?  Answer yes to that question that should eliminate the need to provide proof of insurance unless you had insurance from the Marketplace.

If you had insurance from the Marketplace you will need a form 1095C which is available in your Marketplace account.  If you had Marketplace insurance it is required to enter that information on your tax return.