How can I contact corporate regarding a complaint with Xfinity Mobile?

I have been charged for a phone I do not have for 10 months. I have called and been on the phone for hours with no resolution. I am at the point of losing it with this company. 

Backstory: I ordered a phone on line, Iphone 14Plus for my daughter. She stated she wanted the Pro Max. I called customer service and was told to not take possession of the phone when it was delivered and it would be returned by FedEx. I did just that. The same day, I went to the Xfinity store and purchased the ProMax. Here we are 10 months later and I noticed the charge, yes it took me that long to notice. A ticket was opened, with no resolution. A promise of a callback with a resolution did not happen. Hours on the phone with Tier 2  multiple times with no resolution. They can see a returned is showing processing on my account. I need this resolved asap!!!! I am on the phone with Tier 2 again 1hr and 8 minutes so far tonight.