Bait and Switch on contract renewal

Our pricing promotion period ended in March, so I called to cancel service or to renegotiate our contract. After speaking to the customer retention department we were able to drop some channels and get a lower price that was similar to competitors offers, but still a slight bit higher.  We've always been happy with Uverse, however, so I felt the slightly higher rate was worth it.  Every month since then our bill has come in $50 higher than what we were quoted.  Every month I've called and spent an hour explaining the situation over and over, finally being issued a credit, and promised that a manager would look into it/review the initial taped conversation to remedy the billing issue. Today, yet again, I called to fix the billing error and was told there was absolutely no way I could have been offered what I was offered and there was nothing they could do. We are now stuck in a 12 month contract for a rate that is $50 higher than what we agreed to stay with AT&T for and they do not seem to care at all what their employee offered us as a retention package.  I am livid and completely done with AT&T.  What kind of customer service is this?! It's classic bait and switch. Anyone else have a similar situation with a way to resolve?