When I first joined eBay, back in 1996, it was still being run as a “mom and pop” shop by it co-founders, Pierre and Meg. It’s come a long, long way since back then, and not without a whole host of problems.
One other thing you might consider is to use the Community Boards and make a posting there about this seller.
http://forums.ebay.com/db2/forum.jspa?forumID=107
On that same community discussion board, you will read of others with similar problems as you are having, and the manner in which they resolved the problem.
It is my understanding that once you have reported this seller to eBay Safe Harbor (Trust & Safety) they cannot leave you with negative feedback.
Cheers and good luck.