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If you negotiate with the creditor and all or part of the debt is forgiven or the debt would be canceled under bankruptcy protection procedure - you are sent the form 1099-C.
The amount of debt forgiven is reportable on 1099-C - http://www.irs.gov/pub/irs-pdf/f1099c.pdf - generally is taxable, unless any exemption apply -- you should file a form 982 - www.irs.gov/pub/irs-pdf/f982.pdf - to proof your exemption - and might exclude all or part of canceled debt from taxable income.
Which exclusion to use - depends on the type of your dent and specific qualification requirements.
If you paid the full debt off as you stated above - and there were nothing to forgive - that means - form 1099C was issued incorrectly.
In this case - you need to contact the lender and ask to correct form 1099C. Be sure to contact via certified mail - so if they refuse - you will have supporting documents that you tried to resolve the issue - and will file a formal complain with the IRS.
Let me know if you need any help.