Not on Medicare, but I had a similar experience recently after the July 1 Formulary Update at my insurance company. The sent me letters letting me know that my insulin would no longer be covered unless I went thru a "Step program" with Humalog -- to which I have an allergic reaction! Despite having that information on file, they were insisting I try Humalog for three months. In addition, they told me that because my Dx is T2D, I would no longer be able to get Dexcom supplies thru the pharmacy, but would have to go thru DME (higher co-pay and separate $1500 deductible) -- And would have to go thru an approval process again. Knowing that the DME department already refused my Dexcom twice, i did not expect that to go well. I was left worrying and waiting for the next letter - for my pump supplies...
I contacted my boss and the insurance broker he uses to try and straighten this out. For several weeks it looked like neither one of them would have a solution via insurance (my boss eventually offered to pay for me Dexcom supplies out of pocket if necessary!).
In the end, I got a call from a VP of small business sales at the company who told me to tell my doctor to just put thru all new prior approval forms, and he would see what could be done if anything gets rejected. Amazingly, all the approvals came within AN HOUR of the forms being sent. Since their normal approval process takes 5-15 business days, I have to imagine that this VP intervened in some way.
For now, it all worked out for me in the end, but I am expecting to have to go thru the same process every year. Fun?