Cingular is pissing me off and Helio seems cooler any way

So yeah cingular decided that some how I owe them $200+ for overages but I can't access the bill online that shows these calls and I've requested the bill from them twice now. What I wanna know is how to I go from a 0 rollover min balance one month to a 2200+ roll over min balance two months later and have overage in the month inbetween... ???? something is screwy.