Who are these people?!

My fiance has been getting phone calls from these people for the past three months and they will not give up. They said he owed them $126 from a bank account from years ago. They were adamentely saying they sent him numerous letters saying he owes the money. We NEVER received anything. when he asked them what address they had on file, it was like pulling teeth to get it out of them. Turns out they had an old address from over 10 years ago, and ironically enough, the bacnk account they were referring to was only closed out about six years ago. They were constantly calling and asking for bank account information over the phone and that's when I stepped in. I called them and told them I wanted them to send me a WRITTEN LETTER THROUGH THE US MAIL stating that we owed them the money and they are REFUSING to do so. They said they had no problem emailing it, because "there was no use in wasting trees when they've already sent numerous letters" after I offered to give them our current address & needless to say, he wouldn't let me speak to a supervisor. After this conversation, I ordered all three of my fiance's credit reports and this CA wasn't on ANY of them. Yet, they still insist on calling, and calling, and calling. Finally I told them that unless I get a letter in the mail, they are NOT getting paid. And I told them that if they continue to call, I will have my lawyer contact them regarding harrassment charges.

Does anyone out there know how to get rid of these people?!