Charged for service after equipment return

I switched to AT&T TV on July 28 and returned my equipment on Aug 6 to my local UPS store.  During the AT&T TV activation, I contacted customer service via chat to have my Uverse cancelled.  They advised they would take care of it.  In my next bill, I was showing charges for Internet (no problem) and Uverse for service from Aug 12 through Sep 11.  After three more chat sessions with customer service, I was told by a "supervisor" that I needed to call the 1-800 number to cancel my service.  After getting a hold of the service cancellation person, she said she changed my cancel date to July 28, when I started AT&T TV.  But she also told me that I had to pay the amount showing on my Uverse account but I would eventually receive a credit.  I told her that I will not pay for service that I neither used nor had the equipment to use and I had documentation to prove this.  She said that this is how it works and everything will work out okay in the end.  Best advice, keep copies of all your chat sessions and make notes of conversations with customer service (which I did).