>> Is this real??  <<
What was the subject of the call?
Unpaid loan?

A phone call, email, text message or postcard from a supposed debt collector is not legally sufficient proof of debt.

The Fair Debt Collection Practices Act (FDCPA) includes statements such as this:

Unless the original communication contained this specific information, 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 - US Mail ... not emailed or texted]

Source:
https://www.consumer.ftc.gov/articles/0149-debt-collection

Therefore, if that caller wants you to pay immediately, before you get the written validation notice via snailmail, or if the caller wants payment via Green Dot, MoneyGram, Western Union, prepaid gift card or other untraceable means, then the call is definitely not legitimate.

REMEMBER THIS IF YOU FORGET ALL ELSE:
1.  Legally, THEY must prove you owe the debt (you do not have to prove to them that you do not owe the debt)
2.  They must prove they have a legal right to collect the debt
3.  They must send you snailmail with specific info within 5 days of the original contact, if you request that validation, or if that information was not provided on initial contact.  You have up to 30 days to reply to that validation.

IF you wish to communicate with the supposed collector / creditor, visit  the following page, for example "Action Letters" to snailmail:
http://www.consumerfinance.gov/blog/debtcollection/

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

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Please reply to this post, to let us know you read it, or have taken suitable actions to protect yourself.