From the sound of things, I'd say you've 
definitely got a case.  
I'm not sure how long you've been after the 
seller, but I'd definitely give them a good long 
chance to  respond (sometimes people may not have 
access to the internet or email, so it'd be best 
to give them a fair shot.)  Otherwise, if you 
can't get in contact with the seller, try 
requesting their contact information on eBay and 
getting their phone number, which is much more 
likely to a) assure that you get in touch, and b) 
make them take you more seriously.
If the seller responds, and just isn't willing to 
work something out with you, you should probably 
file a fraud report with eBay.

Best of luck to you,

~Mala