THIS IS AN EXTORTION SCAM. Scammers pretend to be law enforcement (police, sheriff, Feds, AG's Office, fake cop agencies with made-up names) and may be using bought/hacked/phished loan application data to extort money or personal info for fictitious crimes.
The real DEA warns about fake-DEA extortion scams here http://www.justice.gov/dea/pubs/states/newsrel/2010/denver111010.html
The real FBI warns about payday loan extortion scams here http://www.fbi.gov/news/pressrel/press-releases/paydayloanscam_120710
The real FDA warns about fake-FDA extortion scams here http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2009/ucm195814.htm
The real FDIC warns about fake-FDIC extortion scams here http://www.fdic.gov/news/news/specialalert/2010/sa10131.html
Report to the Internet Crime Complaint Center http://www.ic3.gov/complaint/default.aspx , the Federal Communications Commission http://esupport.fcc.gov/complaints.htm , the Federal Trade Commission https://www.ftccomplaintassistant.gov/ and your state AG, as appropriate.
This is a scam. They are calling trying to scare you into making a payment over the phone of 300 dollars or more. Making it seem as if they are going to serve you with legal documentation to go to court. This is not true. They received your information from an online application you may have filled out. Do not give them any information do not pay them. Ask them dates of when you received the loan they are saying you didnt pay back. They will not have that information. Tell them you reported them that you know it is a scam. THey will not call back