Unauthorized charges for a mobile service which I never signed up for

I never signed up for any mobile service, however after noticing dubious charges on my credit card, I reached out to Xfinity/Comcast support. After multiple follow ups to provide me a contract for a mobile service (that I did not sign up for), Xfinity support team apologized for the inconvenience, and they promised to escalate this issue and get back to me in next 5-7 business days (which never happened), meanwhile xfinity support team removed the auto-payment. After unauthorized withdrawal from my credit card for a dubious mobile service (on an old address), I received a collection letter for account number: [Edited: "Personal Information"] (which never showed up in my profile) that I owe xfinity, as auto-payment was removed by xfinity when I requested a mobile service cancellation if it ever existed. This has impacted my credit report, leading to a considerable financial loss.    

Xfnity's actions are highly irresponsible, and I demand an immediate redressal.