Is there a possibility that an amount in excess of the amount owed could be debited from my account or could be debited more than once for the same invoice line item?

Answer:

No. The amounts of the debits are directly tied to the quarterly invoice data and these amounts cannot be altered by the user. The amounts to be debited are based upon the amounts submitted for payment by the user. Once payment for invoice line items has been initiated, it cannot be initiated again either through the Web interface or the batch payment initiation feature. Any attempt on re-initiating a successful payment will receive an error message.