Are you refering to one of the negatives you have left recently.
You cannot edit feedback, seller has to send you a feedback revision request, but how did you pay postage twice?
I would have thought that you might feel more cooperative if seller refunded an overpayment, than expecting you to rely on promises which there is no way to enforce.
It might help to know exactly what happened, as there may be an easy way of getting a refund, but I doubt that contacting ebay would get you anywhere, this dort of problem is between buyer and seller.
