Just download the Xfinity app. You can pay your bill through the app and set up auto pay
I'm not sure about the address as I don't like sending payments through our mail system. But if I were you I'd go to the store and tell them about your problem you've been having for this long period of time and the late fees and maybe they can reverse a few of them(no promises🤷🏿♂️). Also, have them change your preferences in bill payment to more frequent physical bills sent or start paying online, it's so much easier.
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