I sent Cingular a letter through planetfeedback.com and they didn't respond. I sent one through the BBB and I got a call within 2 days of the BBB sending it to them. Since they can't access much of the billing records from whenever they say I supposedly owe them, they are going to send a letter to the CA to remove the balance. The CA should receive it either today or tomorrow and the calls will stop. The Cingular rep to me to call her directly if they continue to call and I should be receiving a confirmation letter within 30 days.
Its a little early but I think I'm calling this a victory for me. I'm just glad the collection never made it to my credit history.

Thanks everyone for all your advice!!