overage don't get charge that way ...it always round up ..example
if you used 250 megabyte as overage it be 1gb if you use another 100mb after that it be another 1gb overage.
If you go over your data limit at all it's going to charge you for 1 GB of data. You get that full GB of data to use until the end of the cycle. You won't be charged for another GB unless you go over the extra GB you've been charged for. Often it's better to make a plan change as opposed to taking the overage, so if you get any more alerts, you can either make a plan change online or call into customer service.