Medicare, test strips, and losing my damn mind

EDIT: I'm T1.

I'm sure some of you know exactly what this is about, or maybe you've dealt with this before. At least that's what I'm hoping. Because I need some advice.

I've normally been such garbage at testing but over the last few years I've been making attempts at getting better, but those efforts keep ultimately getting shut down. Why? Medicare. I'm under Parts A, B, and D, and I've never had issues with Medicare with anything else. Even when I had to get treated for retinopathy last year ($13,000/eye/month), Medicare covered it. No question. Test strips? NAHHHHHH.

(Interpolation: Because I forgot to state it, the test strips in question are the OneTouch Verios, but this also happens with the Ultras. We've tried both.)

Right now I'm caught between Walgreens, my doctor, and Medicare. My doctor sends a prescription for 100 strips/mo (because 50/mo isn't enough at all), Walgreens tries to bill Medicare, Medicare comes back and says "nope, not covered." And yes, they're billing Part B, because for some reason that's what covers testing supplies, not Part D (...which I wish is what would happen because my Part D provider wouldn't do this, but that's a rant for another day).

Now, I was able to get my test strips filled ONCE...back in 2016. Only for one month, and that was after a lengthy fight with Walgreens to get them to send a form to my doctor that had to be signed. Since then? Nope, Medicare appears to be denying everything. OneTouch even says Medicare should be covering these with no problem (since they shout it from the rooftops that their strips are covered by most plans, including Medicare).

The problem now is I have no idea who's at fault. Is it Walgreens? Is it Medicare themselves? The way Walgreens is trying to bill Medicare? That's the infuriating part; I'm willing to get on the phone and scream at SOMEONE but I don't even know where to begin. And if my doctor has to sign off on more paperwork, well, Walgreens isn't telling me anything, sadly. Just that Medicare is straight-up denying me.

Any advice on where to go from here is strongly appreciated, because I'm not sure what to do.