Xfinity Mobil Fraud Dispute

Recently I have been contacted by a collection agency regarding money they say I owe to Xfinity Mobile. I don’t have an account with Xfinity Mobile and have never been contacted by them in regards to any account or charges made to an account. I have spoken with the collection service, C.C.S., and they tell me a dispute claim and investigation are underway at Xfinity. They gave me no other information and I have not been able to reach anyone at Xfinity to update me. My concern is knowing if this is fraud? Billing error? I am totally in the dark and relying on the collection agency to follow up. Please provide me a way to investigate this myself. Thanks for any help you can give me.