Get the name of the firm that the money is owed to -- in our own case, we had a persistent idiot who was undoubtedly a contract bill collector, but calling on behalf of a bank. So I called the bank and asked for the address at which they accepted legal service, which quickly got me to the CEO's secretary. Explained I wanted the address because I was going to get a court injunction against them to stop the harassment, as I was certainly not party to the debt and didn't know the debtor. Wow, did things happen then! She asked me to send her a letter stating I wasn't the debtor and didn't know him, and told me that she would put a stop to it immediately, and gave me her direct phone number if I ever heard another word about it. It's been several years and I haven't heard another word.
Kay