This is definitely a scam, but unfortunately there is not a whole lot that attorneys can do about it for you. But, you should definitely report it. There is a multi-agency task force tracking these things and having some success shutting down overseas scammers, which most of these are. Read more on my blog post here, with links to the reporting agencies: http://www.armstrongattorneys.com/new-payday-loan-scam/
I am licensed only in Texas. Offering information of a general nature in response to a question is not intended to be legal advice in your state.
I have had 3 calls in the past day about this happening. You do not have a warrant; these people are trying to scam you but apparently you were smart enough not to fall for it. Never give out any financial information to anyone over the phone. If anyone may have a real claim, tell them to mail you the information or otherwise to leave you alone.
You and your first three responders are correct that this is a scam. Unfortunarely none have yet provided what you need to know. The FBI is actively involved with these payday loan extortion scams. Here is a link to a recent FBI press release with complaint instructions: http://www.fbi.gov/news/pressrel/press-releases/new-twists-to-telephone-collection-scam-related-to-delinquent-payday-loans
Best wishes for a favorable outcome, and please remember to designate a best answer.
This answer is offered as a public service for general information only and may not be relied upon as legal advice.