I no longer have xshitity mobile and they still have my phone marked as not paid off..

I've canceled my xfinity mobile account and paid off my phone. Ive now sold that phone on ebay and the customer is telling me xfinity is saying its not paid off. Ive waited on hold for about an hour been bounced around from person to person because they "cant handle it" I cant access my account because ive cancelled the account so pretty much xfinity is trying to hold the phone hostage to me and their network. This is after they kept billing me even after I cancelled the account and asked for my credit card to be removed from auto pay. Just awful customer service time after time and a terrible company who have outrageously unethical practices. Stay AWAY!!!!