Have you offered them a way to return the item that is free and convenient for them?
This is a situation where Ebay can't do anything to help you.
You can only keep communicating with the person who has the item.
"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)