You are not allowed to 'name and shame' in here so your post will probably be edited.
The bad news is that there is nothing you can do through Ebay.
Unless you have tracking proving delivery, you do have to accept the claim and refund the buyer.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
