Xfinity Mobile only Fees after moving services

I was overcharged by over $300 over several months after I moved my services to my new address. It seems only my internet was moved and my mobile services were not, so I was overcharged  $25 per lines (I had 2, so $50 per month).

I contacted xfinity mobile as soon as I noticed and the agent assured me I'd get a refund, but it never came. I called a couple more time, and each time I was reassured I'd get a refund but nothing. What can I do at this point?