ATT wireless company ATT DATA PLAN Internet

I having been using ATT wireless phone about 2 years ago and I asked service about my qualify customer. He said I can get off data plan from $30 unlimited to $20 unlimited. And when I can eligible upgrade (I started from 10/2008 and eligible upgrade on July 2010), I can't get it anymore (they already took it out before that they, when the new iphone 4G release). I really get mad and screw up with ATT. Even ATT can change it, but they should tell me before they change it, because I still keep in mind about that guy from ATT told me about $20 when I become a qualify customer, but now I got nothing. Does ATT lie customers?
I wanna sue ATT about that stuff. Not only me but also another customer still waiting for Verizon wireless has iphone. If ATT doesn't have iphone, I never use it.
Don't try to fool customer and earn more money like that way (penalty fees if customers use over data plan). If you have a good service, customers will come to you. That's a way business running.