Consult an attorney. Ask your attorney about your rights under the Fair Debt Collection Practices Act (FDCPA). Be sure to obtain a copy of this act.
Contact the lending institution. If they are still in business, explain the situation and ask for copies of cancelled checks.
Contact an organization such as a bank, credit union or a federal reserve that specifically handles this situation.
Gather any proof of payments. Look for letters from lenders. Gather your past tax returns. Contact the school you graduated from to see if they can verify your loan standing.
Contact the Department of Education or other creditor directly, and provide them with this information.
If the creditor continues to harass you, send them a letter clearly stating that the debt has previously been paid. Your letter should demand they remove your account and personal information from their records; firmly state your expectation to not hear from them again; and warn them that you will consider any further contact as being in violation of the FDCPA.
If the creditor continues to threaten a garnishment action, immediately report them to the State Attorney General and the Federal Trade Commission. You should also retain an attorney and pursue legal action against the creditor.