Yup. Same thing happened to me a while back. Not much you can do. This is why there are so few real auctions on ebay anymore. Mostly all buy it now or set minimum prices close to what they want for an item. Seller just saw he was probably going to be forced in to selling his item for peanuts, so stopped the auction.

That said, you need to tell the seller to initiate a cancelation of the completed transaction if you did indeed receive a notice that you owe for it. He sends a cancel transaction request. You agree to it. Case closed.