Dynamite, you will have to ring them and ring them and ring them until you speak to someone who not only understands you but understands the problem. Emailing ebay is just about useless at the moment - you will get a reply, but from others comments on these boards it may take up to 3 weeks.

Have you contacted the buyer yet? It is worth a courtesy message to let them know that the item is still on its way and ask them to repay once they receive it. Quote the proof of postage to the buyer. You never know, they may still pay once they have it.

Good luck!