@DonnaI729360
It most likely was the doctor that decided to stop doing business with the insurance company (Aetna).
As with any other health insurance you need to pick the best plan for your needs / wants / pocketbook - remember you can change Medicare Advantage plans every year and should always reassess annually because MA plans change especially in network providers.
You will have to set some priorities on your wants for specific doctors or other providers if they aren't all covered. If you are going to make a change in plans, do it during open enrollment because outside of that annual open enrollment period there are only certain special circumstances which will open up a special open enrollment period.
Medicare.gov - Special circumstances (Special Enrollment Periods)
If your MA plan comes with an attached prescription drug plan or if you are looking to change to another that has an attached prescription drug plan, you need to also check that your meds are covered especially any expensive ones.
It's Always Something . . . . Roseanna Roseannadanna