I am pissed

I've just received the records back from USPS that was undelivered to my ebay buyer. I've sold these records 1 month ago and here I've got them back. I've just asked the buyer to e-mail me his/her address and realized that it was exactly the same address that is clearly written on the returned package.
I AM PISSED and have no clue what should I do in this dumb situation.