The numerals are a mere convenience. A bank is required to honor the spelled out amount, because that is what is legally binding. But to the parent's point, pre

The numerals are a mere convenience. A bank is required to honor the spelled out amount, because that is what is legally binding. But to the parent's point, presumably you owed a certain amount before paying, so if you overpaid, you have a credit due. Either way, the terms of the contract remain the same.