It sounds like your current Tax Return Refund was processed before the IRS received and processed your final payment.  If this was the case, the IRS should automatically send you a letter and a refund of the overpayment.  This may take a few weeks.  You can also contact the IRS directly at 800-829-1040.

To be sure your refund was offset for taxes you owed the IRS as opposed to a different debt, you can contact the Bureau of the Fiscal Service (BFS) at 800-304-3107.