Not happy at all

Credence put a collection on my credit report! I immediately called them to see what was this about and they told me that I have a xfinity mobile account! I NEVER HAD A MOBILE ACCOUNT WITH XFINITY!! I've called xfinity multiple times and they don't see anything. This last representative told me to ignore the message. I told them i can't ignore something that was placed onto my credit!! I don't know what to do about this! It's tanked my credit 60 points for something that's fraudulent! And apparently the xfinity representatives can't find the account even when I give them the number that the Credence representative gave me! This is awful I'm beyond [Edited: "Language"]. Do anyone have any suggestions on what to do next?