Legal Research Group, Texas Legal Research Caller was rude and threatening. Texas

My sister recieved a call today from a man who said he was with Legal Research Group, had a TX area code.  He said my sister owed $712 (with fees added) for an internet loan from 2000.  She doesn't recall any loan and doesn't do any business by internet.  He was very rude and threatening in demanding she instagram the money by tomorrow morning or he would issued a warrant for her to be picked up from her job. He wouldnt give her any information about his company or how he got her personal information.  She learned that he had called our sister-n-law earlier and another sister giving them all of the information including the threats.  What have others done in dealing with these scamers?  Please advise.  Thanks, Concerned Sister.