I have been incorrectly getting charged for Xfinity Mobile

I had an Xfinity mobile plan with Internet in my old apartment. When I moved to a new place, I signed up for a new internet plan and cancelled my old ones. My online Xfinity account doesn't show any mobile plans linked to my account. However, I am still getting monthly bills for the mobile account. When I click "View Bill" in the email notification, I don't see any bills because the account doesn't have any mobile associated. I have called Xfinity support multiple times and everytime they told me that they have cancelled the charges, but the still keep coming. I asked my credit card to stop processing payments for Xfinity Mobile and now I am getting a debt collection notice. 

I don't want my credit score to get affected for not owing anything. Please fix this ASAP. It's really frustrating to waste so much time on the phone waiting and getting pushed around from one agent to the other