ACS Law Gropu Phone calls requesting money Clearwater, Florida

I have been getting phone calls from ACS Law Firm for about three month's now. They have left messages for me at work and on my personal line stating that they are going to have the police show up and arrest me and they will throw me in jail for not paying back a cash advance. When I asked about the cash advance they stated that it is through Advance Cash. After looking over my bank statements and not fidning any depoisits from an Advance Cash I asked them to stop calling me since I do not owe this company any money. When I did this the person I spoke with called me a f***ing whore and a dumbass bitch. The people who contact me state that they are attorney's however they all have very thick accents and sound as if they are from South Africa. Has anyone been successful in getting them to stop calling?