Billing continues after service cancellation

I had cancelled my Xfinity service in early September and I have continued to be billed since then. I received notice of this cancellation September 8th of this year (an email entitled "We received your cancellation request", in which they said they were processing it), as well as a phone call that same day confirming the cancellation from the following phone number: (855) 432-0401. Since I received multiple notices of cancellation, I had figured that my Service was, in fact, cancelled, and that I would not continue to be billed, and yet a received a bill in October. Seeing as the cancellation only came through on the 8th, I figured I was just being billed for that limited period of time in September, so I paid it. I have now, however, received a yet another bill due the 19th of this month).

To be absolutely clear: I was lead to believe that my service was cancelled in September via both an email and phone call, and yet I have continued to be billed for the previous two months. How exactly to I get Xfinity to stop billing me for service they seem to be fully aware I have cancelled?