Actually, this firm violates FCRA only if you've spotted something amiss on one of your credit reports. (That's the ''reporting'' part of the Act.) You may have meant the FDCPA, which regulates collector behavior.
The knowledge that you have active legal rep for the account should end the call immediately. It's unclear from your story if you had the account discharged or beaten down in a prior suit. I would say you can hose this new collector in court if you've documented the call well.
Anyway, it's possible you've somehow attracted a fake payday loan collector. Shrill threats and the lack of a valid business name would be matching attributes. Your defenses are then reduced to complaint submission to the FTC and attorneys general. The FBI is also taking comments on this category of thug via the Internet Crime Complaint Center:
See discussions for these numbers to see if their stories match yours: 704-200-9909, 559-823-5337, 813-441-0108, 443-451-3816, 496-656-7520