Help.Phone co. overdrafted bank account

[Shan]

I live in Kokomo Indiana. I called and canceled express pay(debit out of acct.) because of problems with phone co.(AT&T) trying to get more than I owed and also debiting at a wrong date. I just wanted to pay by mail from now on. They went ahead and took money out of my account anyways and I did not have the money to cover what they did, so now my account is overdrawn and I'm paying my bank $111.97 . I need that money for my rent and other bills. I called the phone co. and they told me "sorry for the inconvenience" "theres nothing I can do." Why do I have to pay dearly for their mistake. How is that legal? Why don't the little, poor people have any rights or justice against the big companys? So I guess I'm asking if theres a law that makes them responsible for their actions and mistakes? What to do? Shan 8-5-08