Thread:Paul.rea/@comment-4802762-20150319201419/@comment-4091815-20150320004328

Block the following as if it was a single user - 109.111.237.0/24

That is the range in which your problem IP appears. You will be blocking a few hundred people in Serbia as well but it will force your target to change proxy.

Once he does you'll need to block the new range too.

I've had success with this technique before - it might take a few blocks but soon they're out of proxy options and you have a pretty good map of proxy IP ranges blocked to avoid future problems with other bad users.