Did you get any kind of notification from the seller, after the auction closed? Some sellers have their Paypal account under a different email address, for some reason; an "unclaimed" payment has something wrong somewhere. Email the seller through eBay's "ask the seller a question", and maybe they'll answer that.
I sold a purse once, and the buyer made a typo in my Paypal address. She kept emailing me, telling me that Paypal told her I would have to open an account to claim the payment, and demanding to know what Paypal told me. I think she was mentally "challenged" because after a few days, her sister emailed me, told me there was a typo, and made the correct payment. I could tell something wasn't quite right, so I tried to be very patient with her, and I was glad later that I had.