First contact the seller from the original listing. It's on the right side.
If that doesn't help, and help is a refund or a tracking number, not a promise of a replacement, go to the eBay Resolution Centre at the bottom of this page.Open a Not As Described dispute.
You can skip the Contact Seller suggestion. You've ddone that.
The seller will be required to send you a Return Shipping Label.
If he doesn't he loses the case and you will be refunded.
If he does, return the item you did receive*, and you will be refunded in full.
But start with the seller.
*Yes. I understand.