The due date on the current bill doesn't apply to the past due amount. If you have a past due amount and haven't already paid it, then you should, as soon as possible. Don't wait until the due date of the current bill to pay the past due amount. Why? Charges that remain unpaid can result in late fees and/or suspension of service, and late fees may be charged each month for any eligible unpaid balances not paid in full by your next bill date.
If you sent a payment but we didn't receive it by the due date, you will see the previous balance on your current bill. In this case, you only need to pay the new charges.