Have you checked the tracking on the Royal Mail or courier website or just on Ebay?
Unless the seller receives the item, they won't have to refund you and you may have to claim against the courier for the lost 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)