Oh my! I would call the insurance company, for sure. Get everything in writing. Information you communicate to them and the information you get from them. If they persist in trying to collect money they are not owed, which is exactly what they are doing if they make up fees and lie about documented treatment, consider reporting them to their professional organization, the State board, and consider an attorney.
After our son's birth, the hospital tried to rebill us for services already paid by insurance companies. At first, they gave me a hard time and threatened collections and such, claiming it was a different bill (for the mystery 2nd baby?) or that it hadn't been covered. So, I had our family attorney call back. Done in about 30 seconds. I don't want to sound litigious, but without the threat of legal action, they probably would have kept hounding me.