Good health insurance attorney

Like the title says, I had surgery almost a year ago and have been battling my insurance company over the claim which the hospital said was approved beforehand. I’ve appealed and they’ve denied the appeal changing the reason for the denial from “non disclosed diagnosis” (which my long term doctor wrote a statement attesting to the fact that it was not) to “not covered by your plan” and “after termination of coverage”. The surgery happened in August of last year while I was fully covered, I no longer have this insurance as of April of this year with my company changing carriers because this company was garbage to all of us, but can they really deny coverage for a surgery performed during coverage but appeals going beyond the term of coverage and change the purpose of the denial, like What does not covered by your plan mean? It was a common procedure for women of my age. I’m so confused and lost and feel like I need and attorney. Any recommendations?