This may be the usual dirty debt collector within the U.S. or a fake collector from South Asia. Either way their empty threats of arrest, imprisonment, lawsuit filing, and/or asset seizure violate federal and state laws. Try to get a business name and share it with the readers. By federal law this name cannot be withheld.
Learn how to exercise your FDCPA rights as an alleged debtor at FTC-dot-gov.
On 800Notes in the ''Debt Collection Calls'' forum is a thread titled ''Fake payday loan collection scams - Please list new numbers here ''. My notes and advice on the payday loan collection thugs, updated Oct 2011, can be seen on the lead page.