Then again, you must be on Medicare ADVANTAGE and not Regular Medicare.
I have never once had a referral to go to a specialist and Medicare has paid every claim that was submitted by those specialists.

Straight medicare does not require a referral or even preapproval. With my medigap plan I also have zero copay for anything tho I'm totally aware being able to afford the $180/month for the medigap supplement is a luxury not everyone can afford. Medicare advantage plans are a nightmare for preapproval and getting worse but they offer perks to drag people in. If you don't take medigap within 6 months of turning 65, chances are you are stuck with an advantage plan the rest of your life.

But if your doctor denies you care, call your insurance company, next insurance commissioner, I've gone as high as the DC office of social security where the call came in as "US government" and they fixed things pronto.

Never accept no but you have to be willing to become a bear for self advocacy. If Your PCP is open to a lawsuit, they can continue to refuse you care. See I'm the type who would just say that to my insurance company, not necessarily the doctor as she could throw you out before you have someone new. I'm so sorry. They are not kings, queens or gods probably much to their chagrin. We have options. Just keep eating up the food chain. Your PCP is at the very bottom of the food chain tho they font want to think that, they are the one with the least power, not the most. At least in the US.

I've can tell you stories of things I've done for care that woulf curl your toes, but they worked. One even to reverse a terrible social security error and they were about to stop my checks in weeks and make me homeless. You would never believe what I did. My next check was 10 days late but their mistake didn't make me homeless. Never accept no from a doctor. "What do they call the medical student who graduated last in their class? Doctor!"

Medicare doesn't requite referrals but many specialists do. But an ortho walkin clinic can give you one. I did that this week. Spine dr wouldn't see me until someone else ordered an MRI. My PCP would have but I wanted an eval first and the exact right MRI ordered.
My best. Be

You are on Medicare Advantage, an HMO, which is a total disadvantage to the consumer. Regular/Original Medicare doesn't require referrals to see specialists. I've had a back, hip, SCS implanted, shoulder and neck surgery - I went to the doctors/surgeons of my choice. Hopefully you can change at the next enrollment period 10/15 - 12/7. Preexisting conditions are covered by regular Medicare. Shop for a secondary policy (picks up the 20% Medicare doesn't cover) through a private insurance agent/broker to get the best rate.

I'm sorry you are going through this. I'd get a new PC doctor.