To make it very clear.

When an item sells ebay send an email and there is an address given, this will either be thye buyer's premier delivery address or the last one they used, a buyer can have several addresses linked to their ebay account.

That address is not confirmed as the correct delivery address until the buyer goes through checkout, nthey can choose any delivery address at that stage. The address given in checkout will be the one now seen in view order details and in Paypal.

You have to send to that address with a qualifying level of tracking in order to have seller protection.

The buyer has done nothing wrong, you sent to an address that was given pre checkout completion. There is no way you can get your money back from anyone, I hope it wasn't too expensive a lesson. Keep your fingers crossed, if your return address is on the parcel it may get sent back to you.