Need to stop auto pay

I need to cancel my Xfinity service and stop auto pay.  The past two days was the worst customer experience I had with Xfinity.  Called many times, tried all the online support, can’t fix my internet connection and can’t connect me to a live agent.  Need to cancel the service and can’t do it via the app.   Please let me know how I can cancel my service and stop the auto pay.  Thanks.