AT&T Unable close account St. Louis MO

I canceled my AT&T U-verse service by phone in St. Louis effective Sept 24, 2014.  At the time we did not have a balance due because they bill in advance, and our last payment was late August.  At AT&T's direction we shipped the equipment back to them via UPS.  This was done on September 24.  Then in Early October we received a bill for $317.  We phoned AT&T and the rep agreed it was an error.  Said do not pay the bill and we will send a final statement "in a couple weeks".  That did not happen.  Instead we received a new bill for $480.  This prompted a third call wherein the rep said that a manager would call us back that day.  That did not happen.  We originated a fourth call from the local AT&T store in Gresham, OR where we now live.  The result of that call was again acknowledgment of the billing error and a promise to correct it, and properly close the account.  They also promised a confirming email.  Neither has happened.  At this point I think AT&T's actions border on criminal.  I expect their next fraudulent activity will be to report us to a collection agency and/or a credit bureau.  That of course would mandate litigation, which is in nobody’s interest.