I prefer drawing and quartering, but thats just a personal favorite of mine.
Seriously though, do a whois search on them, and send a Cease and Desist letter to as many methods of contact as possible. You can get stock C&S letters
here. I would personally add in a line about them being responsible for notifying you of the removal, and if they haven't done that within the 72 hours stated, start by sending it to their ISP/Hosts and move on from there.