My insurance company does this periodically.
1. Get a detailed copy of your policy. Specifically, what is covered. Detailed. They won't want to give it to you...
2. Get, in writing, the reason it was denied. Half the time it's a code issue but get the details.
3. Call the accounting depth of your doctor's office. Make sure that the diagnosis and treatment is correct,
4. If it is a code issue, call insurance, then doctor's office, then insurance then doctor. Keep going until it is fixed.
5. If it isn't and your covered, your plan has an appeal process. Follow it. Complain to the state insurance board. Depending on where you live, there are other state offices as well.
If you need help, PM me.
Jen