Once a buyer goes through checkout to get to Paypal the address in Paypal will be that which was showing in checkout so it is impossible to send to the wrong address unless you go by the item sold ebay notification sent as soon as the item is purchased.

I would not have contacted ebay, that just complicated the problem. You had, and still have, Paypal seller protection as long as you sent to the checkout address so if it were me I would ask the buyer for the cost of tracked and insured postage to resend it or the offer of a refund less original postage and ebay fees.