AT&T Chat Failure & No Customer Loyalty

In early June I used AT&T's online chat hoping to extend my U-verse current promotion and was told by the agent that they had talked to a specialist and that my current promotion would continue for another 12 months, yet I later found out that the agent failed to complete the promo extension as promised and by the time I realized this the current promo was no longer available leaving me to pay hundreds more per year.  This feels incredibly unfair since the error was made by the AT&T agent.  However, all calls I've since made to AT&T customer support have said that they cannot see the chat records nor do they have a way to receive a copy of my chat record, so there is nothing they can do other than offer me a 1-time $10 credit.  I feel highly betrayed and unvalued after being a loyal AT&T TV/Internet/mobile customer for many years.