Woman speaks in Legal mumbo jumbo about the need to serve me papers at my place of employment.....idle threats

I got the same call she threatened to serve me with papers if I don't give her 600 dollars today

They say they're City Management Group legal department. Have received several voicemails from them (from a different local number but I'm told to call him back at this number) saying my name (which they never addressed me by) and number are attached to a felony fraud complaint against the guy who previously had my phone number. I've had this number since 2007. They keep threatening that if I don't "give him up," a decision will be made that will not be in my best interest.