Are you sending the messages via ebay? You can't reply to the auto-send ones sent to your email address by ebay but instead go into your actual Messages in ebay or Contact Seller from the Purchase History.
If the seller is truly non-responsive after 24 to 48 hours, go immediately to paypal and open an Item Not Received case in the Resolution Centre. Find the transaction in your Account Activity and go form there. Pay careful attention to the instructions for claim versus cases and the associated deadlines. Above all, do everything paypal tells you to do by the time they tell you to do it.
And DO NOT accept an offer for replacement from any seller overseas. This is often (although not always) a stall tactic designed to time-out the resolution process.
Best of luck to you.
