Retention department not honoring contract

I called the Retention Department in July because I knew my contract term was expiring and my "introductory rate" was going to expire.  I spoke with Efram and he told me the increase would be approximately $80 per month.  I, of course, told him this was unacceptable and after many back and forths, we settled on an increase of $18 per month with no changes in my service.  

Two months later I received my bill and the increase of $80 was what I found.  I called customer service and was told that there was no documentation of any conversation with Efram in July.  

I subsequently spoke with Brian, a supervisor in Retention, who also told me that there were no notes from conversation with Efram.  I had taken notes however, and rattled off all of the details that Efram had given me to which Brian responded that "that offer does not exist " and he cannot offer it to me.  He could however decrease my services to get me to that rate or he can keep my services the same which would be an increase of $40 per month.  

He went on further to tell me that offers change all the time - to this I suggested to him then that the offer that Efram gave me back in July probably did exist then in July and that AT&T should honor it - his answer was "NO".  

This is AT&T's mistake and I am paying the price for it- they should train their CS people better and give their supervisor's the authority to make decisions that will retain customers - especially if you work in the Retention Department.  Stand by your offer, AT&T!