Give a list of their IP's and contact information to Spamhaus http://www.spamhaus.org/. If it's bad enough they will hold the ISP's IP's hostage until they get rid of the customer. If they decide not to stop, they could contend for a spot on their "ROKSO". It still won't stop them, but it will at least cost them time and money to get new servers and ips. Also send samples of the emails you receive to their ISP's abuse department. If nothing else you'll make them unhappy for awhile.

Instead of using their personal email addresses to sign up for spam, just use spam-trap emails to sign up for their own crap. If that doesn't put them on the radar, you could always resort to weeping in a dark corner somewhere.