This is where the Fair Debt Collection Act comes into play. First, ask the called for their name and company contact information. Write it down for your records. If the person on the phone refuses to give it to you, the call is likely a phony. By law, the collector needs to identify him/herself. Next, if the called says they need to confirm your information, don't give out or confirm your personal financial or sensitive information unless you have confirmed this caller is legit. Reports show the scammer like to take the personal information they obtained about you and use it to commit identity theft. Maybe they will open up a credit card in your name. Tell the caller you need written proof of who they are, which is called a validation notice, before you will talk any further. If the caller is real, they must send you a validation notice within five days of when they first contact you. This is the law. You then have 30 days to dispute the debt.
Read the following article for more helpful information on dealing with a debt collector