Hi Catherine, how did you approach ebay support with this, through a documented email or live support?
The sort of response that you received sounds like it may well of come from live support. They can be helpful at fixing small issues, but their job is to service online inquires as quickly as possible, and will often just dump something like this in the too hard basket.
By emailing your concerns to support, documenting all of the evidence, you will be able to open up the lines of communication with a rep, and have a far better chance at stating your case.
If that is the response from customer support to well documented email correspondence, then I wouldn't be letting it go at that, I would be asking for complete clarification as to their policy, and as to why they were prepared to let someone get away with what has happened here.
I would be at the very least be demanding a review of their original decision. You can't let this type of thing consume you of course, the longer you trade on ebay the higher your chances are of coming across complete a-holes that are just out to screw up your day.
Use the feedback response option, although with the limited amount of characters your are allotted, you may have to get very creative with your writing skills to make your point effectively.
Btw, did you confirm with the supplier that the description of the product you listed was in fact accurate, if you're going to shoot, you need to make sure you have the right ammunition.