You will have to make a claim against the carrier.
It is up to you to refund the buyer, then go to DHL for a refund.
(Unless you used Ebay Simple Delivery.)
What does the tracking show?
"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)