A debt collector called me & threatened to have me arrested for loan Freud i never recieved

I got a call from a guy stating he was a federal agent & that i was being charged with 3 criminal acts of Freud & that i would be arrested on 7-8-13 if i did not pay a $300 loan that i never recieved. He calls my office 20x per day & harasses my coworkers for information. He also is using my cell phone # on his caller ID (impersonating) myself so the office will pick up the phone.