If you send the debt collector a letter stating that you don’t owe any or all of the money or asking for verification of the debt, that collector must stop contacting you. You have to send that letter within 30 days after the debt collector first contacts you, either by phone or by letter as the first contact. But a collector can begin contacting you again if it sends you written verification of the debt, like a copy of a bill for the amount you owe. (See our Letter for Debt Validation)