There is not anything anybody can do to help you.
You had 30 days to return the phone to the seller using the Ebay Money Back Guarantee.
As you have now sold the phone and don't have it to return, you can't start a chargeback with your payment provider.
I'm afraid you will just have to write off the loss.
"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)