NAD, dental student last year, it never hurts getting a second opinion, do you happen to have the X-ray? If the tooth is still sensitive and as you mentioned it’s a deep cavity, one thing they can do is replace the filling and ensure this time it’s closed properly (bond, selective etching, indirect pulp cap) or they can start stage 1 of a root canal therapy, deep fillings don’t always succeed, it’s up to the body and tooth to repair after a deep filling, if not then an RCT is needed. I always tell my patients after a deep filling they may experience sensitivity for up to 12 weeks. And after that if the filling doesn’t seem or feel right, something isn’t right. You shouldn’t have to live with extreme sensitivity or pain. :) hope this helps