Did you open an Item Not As Described Dispute?
Were you instructed to return the phonecase to the seller?
Were you told to use Confirmation of Delivery?
Did you use a service with Confirmation of Delivery?
Did you put the tracking number into the Dispute?
Did you update the Dispute when the tracking showed delivery?
If you didn't,eBay will not refund you.
You can try going to the Paypal Resolution Centre,
Again you will need proof of Delivery, but you have 180 days from payment for the Dispute.
And if all else fails, you can try the credit card you back your PP account with.
Phone the 1-800 number on the back of the card and ask about chargeback.
Different cards have different standards.
Some have shorter chargeback times.
Some will accept proof of shipping instead of proof of delivery.
But every company that handles the dispute will need proof that the item was returned to the seller.