Did you have a postage cost listed? How is ebay supposed to know it was pick up? If the buyer has collected, send an invoice removing the postage cost and send. Don't hit recalculate. Let the buyer know to ignore it. Then go back to the item on your selling page. Refresh the page, make sure the postage now says $0 then mark as paid, then posted. Any fee that had been charged for postage will be removed. If you had already marked as paid and posted, you need to ring ebay to get them to refund the fees.