Error from comcast when canceling my mobile service

I’m not exactly when sure because I just moments ago realize this. But I changed my phone number to a different carrier and canceled my service almost a year ago. It seems like and I literally just noticed that they have billed me every single month since I am furious I cannot stand Xfinity service on any scale or platform their customer service is awful, and they seem too greedy to even do their job . I demand a refund immediately. I have all The proper paperwork and receipts from when this changeover took place