Your purchase is protected in several ways.
If your purchase was supposed to be delivered* more than 30 days ago, or if the seller was closed down by eBay (NARU - Not a Registered User), then you cannot proceed with a dispute.
Instead you go to your Paypal transaction.
Find the payment and copy the transaction number.
The PP Resolution Centre is at the top of the PP account page under Tools.
Open an Item Not Received dispute and immediately escalate to a Claim.
Don't bother trying to contact the seller. That time has passed.
If the seller cannot prove to Paypal tht the item was in fact delivered, you will be refunded.
If you did not use PP, go instead to the 1=800 number on the back of the card you paid with and phone about a chargeback. Cards have Buyer Protections, but they vary from card to card.
*Last estimated delivery date plus 30 days.
