Complaint Review: acs debt collectors

Caller continously calls my place of employment after I have requested several times to have them stop, that I wanted to dispute the claim because I have no record of ever taking this loan out. The bryan nelson that I spoke to refused to answer any questions and told me that if I did not make a payment then he would continue to call my work. I told him I would call him when I got home and he told me until I paid off the debt then he would continue to call me at work and not at home. I was so upset. This is the detremental to my job and I explained this. I have not even had a chance to verify if this is valid because I have not gotten any type of material or documentation from them.