Xfinity is continuing to bill me after my service was cancelled, multiple times

Seriously this has to be outright fraud. It has been only 3 weeks since I cancelled my service, a task that took me over an hour and 5 call transfers no matter how direct I was, and now I have recieved bills for not only one month but 2 in the mail. I removed my billing details and cancelled autopay, and gotten the confirmation email confirming my service was cancelled on the 1st of the month, at the end of my last billing cycle. Now I am getting letters to my house asking for money for service for January AND February. I have no comcast equipment or contract and previously I tried chatting with a live agent, who confirmed my service was cancelled on the first and essentially gave me a "don't worry about the bill" anwser in some long-winded way saying that comcast was billing in advance by mistake for January. 

I don't know how to get them to stop billing me for a service I don't have, and also how frustrating it is when a company tries to claim you owe them money deceptively. I have no doubt that they would readily take payment if I sent it to them, which seems like clear fraud, and I don't know how "just ignore it" is an actual anwser by a customer service agent. This hardly seems like a mistake and it's a nonsense anwser to say "we can't stop the billling robot it has a mind of it's own", comcast and xfinity need to stop billing me and wave any bill that is currently out there, I owe them nothing and I have no service or contract with them. I doubt I am the only one experiencing this as well, so if any one has any way they've dealt with this please let me know.