There's a thing in eBay to make resolutions like this, where you make a complaint in a forum between you and the other person, and there's also an eBay moderator. I've used it once 2 years ago and it worked. It forced the seller to answer, mind you in my case I had already paid and he wouldn't answer so you're in luck. You can also allways make an offer to the 2nd highest bid I think.
