It's important to know when you bought this item.
Are you still within 30 days of the item's last estimated date for delivery, was it cracked on receipt of the item? Then, message the seller no more if they are not replying, just proceed this way.
Go right of the item in your Purchase History and from More Actions select... Return this item selecting the reason Item Does Not Match Description or Photos.
The seller needs to accept this case within 3 days and refund, if they want their item back first , they need to pay for that fully tracked return postage, then on receipt of their item they have 48 hours to refund you. If they don't , need to escalate the case, ask eBay to step in, and they'll force the refund.
Never listen to any excuse or promise from the seller to close the case early, and do not forget to escalate.
@laurgo_74
