This is simple. Get a copy of your credit report from annualcreditreport and find out their address and contact info. Contact them about paying it, and do so. (If it's the Dept of Education, look at the bottom of this post for a link.)
Student loans are absolutely the WORST things to not pay.
Per ed.gov:
Once your loan is assigned to a guaranty agency or the U.S. Department of Education (Department) for collection, the following steps may be taken to recover the outstanding balance due:
* The Department of the Treasury may offset your federal and/or state tax refunds and any other payments, as authorized by law, to repay your defaulted loan.
* You may have to pay additional collection costs after your loan is assigned to a private collection agency for collection.
* Also, you may be subject to Administrative Wage Garnishment, whereby the Department will require your employer to forward 15% of your disposable pay toward repayment of your loan.
* Federal employees face the possibility of having 15% of their disposable pay offset by the Department toward repayment of their loan through the Federal Employee Salary Offset Program.
* The Department may take legal action to force you to repay the loan.
* Finally, credit bureaus may be notified, and your credit rating will suffer.
Once a loan is declared in default, you are no longer entitled to any deferments or forbearances. In addition, you may not receive any additional Title IV federal student aid if you are in default on any Title IV student loan until you have made payments of an approved amount for at least six consecutive months. Please see Going Back to School for more information on this topic.
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Also note that defaulting on a gov't student loan pretty much bars you from any gov't job or entitlement. It ranks up there with "Are you a convicted felon?" in the government's eyes.
If the defaulted loan is held by the US Department of Education, there is information here on how to make payments:
http://www.ed.gov/offices/OSFAP/DCS/repaying.html
Good luck!
TU - 688 | EQ - 664