You had a winning bidder so as far as ebay are concerned you sold it.
Ebay charge the final selling fee to your ebay account as soon as the listing ends with a winning buyer not when the buyer pays.
If the buyer doesn't pay or you have to cancel the sale for some reason you have to make ebay aware in order to get a refund of the fee.
You need to send the buyer a cancellation request in order to claim a refund of the seller fee.
