Oh boy, that is a really good question. Since your doctor has filed multiple times with no luck, I think the only choice you have left is to go the appeal route....and it can't hurt to try. This link might be helpful and it does point out success rates for the appeal process. The link is....https://www.additudemag.com/adhd-medical-insurance-battle/
I wish I could be more helpful. Do let us know how things work out. I have a feeling that your case will be becoming more common in the years ahead.
Good Luck!