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How to challenge the validity of a debt
Find any information you have in your own records about the supposed debt.
You may not have anything, but if you do, you may be able to use it to your advantage down the road. This includes purchase agreements, statements and other pieces of information you have in reference to the alleged debt.
Draft a debt validation letter to the collection agency. You must do this within 30 days of the original letter you received from the agency or else you will lose your chance to dispute the debt.