Cannot Cancel a Xfinity Mobile line

I've been on the phone multiple times for multiple hours, just trying to cancel a line. This is for a phone I brought myself, so its not an issue of paying off the phone. 

Each time, a rep assures me it will be done, and then it is not done. I call back , and they say there was some error, and for sure it will be done this time. Repeat over and over again.

If I cannot cancel this line, i will keep getting charged taxes and fees having this line open.

Can someone please help? Pretty sure you cannot force someone to stay on your service just because you can't figure out how to cancel the line.