They're also called CACH LLC and, I believe, CACV LLC. My gf has a collection account from them on her report. She sent 3 DV letters, hasn't had a response on any of them even though they updated her credit report as of a few days ago.
I have heard that they agree to a PFD once you document their violations, although in your instance you've already paid the account so that wouldn't work. I doubt a DV would get you anywhere, but it's worth a try. They might get rid of it if you dispute with the CRA's though.
How long ago did you pay this?