Medicare Advantage isn't a service - it's an HMO. I don't know which HMO you're associated with, but you might check and see if one of their medical organizations can do a better job for you.
I had to bite the bullet a few years ago, quitting my $21 a year Medicare Advantage plan because they were a hassle to work with, didn't include my cardiologist in any of their provider lists and, as I said, were a real pain to work with.
I'm now paying almost $300 a month for my Supplement - but it lets me use my cardiologist, go to pretty much any doctor I choose (without needing a referral and waiting to find one who works with the Advantage plan), and get needed tests and diagnostic procedures without having to get them approved days later by an employee whose main purpose is to cost the employer as little as possible to provide appropriate care).