I just got a letter from the IRS saying I owe my return to a previous year debt. I already got my refund Visa card. What's next?

[DanO]

Verify that what the IRS used to calculate that you have a tax liability from the previous year is accurate. The letter should explain the discrepancy and you can double check how you arrived at you figure.

If you are in agreement with the IRS, then send the a check or go online make a payment.  If you don't agree then contact them with the phone number on the letter and see if you can come to a resolution, or the next step.