how do i handle a call from someone who claims to be a collector on a payday loan from 2003

Received phone call on my job from someone who stated I had committed fraud related to a loan from 2003 (13 yrs ago) which amounted to $1700 some odd dollars due to accumulated interest. He was unable to provide any details about the lender, but that the references listed would be summons to appear in court to testify if I had their permission to list them as references. To keep this from going to court I could make a commitment to pay thru Western Union or a prepaid credit card and that I would receive an email stating that payment has been received and an electronic signature would be required and returned to them. He frightened me with all that he said and I provided him with a pre-paid card# and agreed to make a $300 initial payment that evening. I have never received any mail regarding this outstanding balance nor does this appear on any of my credit reports. I discussed this with a friend and was told that this may be a scam and I immediately cancelled my pre-paid card. Per the caller ID the name of the company he represented is National Assets, with a 470 area code. I tried calling the 800# he gave me and they do not have anyone with his name that works there. Please advise.