Why Does At&t Lie To Customers

I started using u-verse home phone, internet & TV two years ago. I cancel my TV service due to functionality problems. (kept loosing signial) my internet same problem. After hours & hours on the phone with tech's, I was told by a level 3 tech I was on the wrong chennel. No more problems after that. during the two years without U-Verse TV, I received numerous letters from David Banks with a special offers to customer that was already using  your Internet/phone service. After talking to three rep's to be sure, I understood the offer of 67.00 for services for six months. You posted my first bill for 256.00. This is a total lie of what the letter from David Banks had written in his letter to me. Special offer code AH58-0803 AU20QQ812-T3-US-L3-T3