Unitedfastcash500 call and harass about a loan i never took out. wont give me any information, wants payment with check or debit card, had my social wrong, wont send me any paperwork, but says my social and name will be Internet

These people keep calling me at my job saying i took out a loan with an Unspeciafied company. At 1st they said unitedfastcash500. I said I ahve never been contacted by anyone about this. She was rude and said well you are now. They had the last 4 of my social wrong. She wants me to give payment over the phone with out her sending me anything to verify I owe this debt. She said if she has to send paperwork, it will be to the APD ( Austin Police Dept ) and I will be arrested on fraud charges.
How do we get this stopped. I never took out any loans. and the one's i did i paid back.