Xfinity Mobile Billing Fraud

I'm requesting help with my mother's account. I noticed last month that she had a $347.00 bill for her mobile account. Turns out someone has been using an added line to her account. I tried to discuss the issue with Xfinity phone support, got transferred 4 times and after an hour they hung up. We immediately booked an appointment with the local store, and they said to call the Mobile support line. They did not want to help with mobile service at all. Once again, I was forced to speak with mobile support and have spent hours repeating the situation. We were told she was entitled to a $2000 refund and someone from Xfinity would contact us with a resolution in 10 working days. Never happened. I was asked why it took so long to detect the additional line. I mentioned she’s 91, has autopay, and never questioned it. Now I’m involved as the manager of her account and I’m livid about the poor support and lack of interest in resolving this issue. I don’t want to escalate this to an Edler Financial Exploitation situation if I can get some help from Xfinity.