Firstly - a word of caution.

When using Paypal it's important to understand their rules, seller protection etc and NEVER to accept a payment for more than you can afford to lose.

When accepting a payment you will only be covered by the Seller Protection if you have jumped through the several hoops involved.

IE

Sending to a confirmed address and ONLY that address (not any other address that the buyer give you)
Sending by a means that it online trackable (which I note you did)
Ensuring your item is not deemed "intangible" by Paypal.
Ensuring the transaction is marked as "eligible" for Seller Protection.

It's obvious now that the payment was made either by someone knowing all the above and being pleased you fell down re: Seller Protection.

OR

It was made by someone who somehow had access to another person's ebay/paypal account.

I echo callumsgran's advice.

Go to the Police with all your print outs and the name and address that you posted the Bonds to. This is FRAUD and don't be fobbed off. They have received goods by deception. SOMEONE signed for the envelope!

Re: Your ebay account. NEVER leave feedback until you have notification from the buyer that they have received the item and are happy with it. Payment is NOT the end of the transaction.

Re: The person whos stolen bank card it was. NO you can't claim against them. THEY didn't receive your item!! The Fraudsters did!
(How would you feel if it had been YOUR card?)

You need to report the theft/fraud to the Police asap.

Good Luck.

PS And PLEASE read up on Paypal if you are going to use it for such large sums. The Payment & Postage forum in the ebay "Community" is a good starting place for advice.