Your seller is incorrect. Of course he can resend it if he wants, either as a new delivery through Evri or by post or other courier. Or he can simply cancel the sale and eBay will return your payment.
If they won't do this you will not be able to file a claim through eBay as they treat attempted delivery as being successfully delivered - even though it wasn't.
If you paid by PayPal you can file a dispute under their buyer protection policy. (PayPal requires tracking proof that the item was delivered, not just that it was attempted.)
Otherwise, you may be able to claim from your payment provider, e.g. credit or debit card issuer.