Step 1: get the collection in writing
Within five days of first contacting you, a collector must send a validation notice. If you request validation in writing within 30 days, they must stop collecting until they verify the debt. Always request validation — it is the cheapest leverage you have.
Step 2: compare the collection to the original account
Pull all three reports and line the entries up. Look for a different balance than the original debt, a date of first delinquency that resets to when the collector bought it, the same debt reported by two agencies, or an account that was already paid or settled.
Any of those is grounds for a dispute with the bureaus and the furnisher.
Step 3: dispute what is wrong, negotiate what is right
Send a dispute to each bureau reporting the error, with copies of your evidence. The bureau has 30 days to investigate. If the collector cannot verify the item, it must come off.
If the collection is accurate, disputing it will not help. Then the conversation is about settlement terms and, where the collector allows it, how the account is reported after payment.
