Collector contacted you about a debt? Under FDCPA §809(b), you have 30 days to demand they validate it. They must stop all collection activity until they prove the debt is yours, in the correct amount, and that they have the legal right to collect it. Many can't.
You must send this within 30 days of their first contact for automatic collection-activity-stay protection.
Cites FDCPA §809(b) correctly. No "609 letter" garbage.
CERTIFIED MAIL ONLY. Proof of delivery = proof of your timely demand.