Go to your Paypal account and copy the transaction number there.
Go to PP's Resolution Centre at the top of your PP account page under Tools.
Open an Item Not Received dispute.
You have 180 days from payment from this.
You have already attempted to contact the seller, so skip the suggestion (and with both eBay and PP it is just a suggestion, not a requirement) to Contact the Seller.
Escalate to a Claim.
If the seller cannot prove delivery (not shipping, delivery) you will be refunded.
In future, don't get into a conversation with the seller about this.
Just ast "What is the date of shipping? What service was used? What is the tracking number?"
If the seller ignores you or does not give you a tracking number or tries to put you off for more than a day or two, ask eBay (or PP) to step in and escalate to the Claim
If the seller cannot prove delivery (not shipping, delivery) you will be refunded.