Phone calls are meaningless - DEMAND written proof of this "problem" that is MAILED to you. They then have 5 days to comply. NO emails, texts, faxes, etc.!!! Expect excuses and possibly illegal threats but no paperwork. Give your state attorney general a call too.
BTW - refusing to give a company name & address is a violating of the FDCPA!
Just had them call my mom with some of my personal info stating that they were lawyers and I was being sued they wanted me to give them my address and make a payment from a jcpenny are I never had from 1999