The Fair Debt Collection Practices Act (FDCPA) includes statements such as this:
* Every collector must send you a written “validation notice” telling you how much money you owe within five days after they first contact you. This notice also must include the name of the creditor to whom you owe the money, and how to proceed if you don’t think you owe the money. ["Written" means snailmailed ... not emailed or texted]
If you KNOW you owe no money, or believe the call was from a fake debt collector, please take the time to read this:
http://www.consumer.ftc.gov/articles/0258-fake-debt-collectors