It's not true that there is nothing you can do. You should contact ebay and ask for the neg to be removed. If you provide evidence that you have been reasonable and the buyer is not responding I am fairly confident they will remove the neg. They did it for me but they had to be satisfied that you tried to communicate with the buyer first to try and resolve it. Seeing as you've done this I see no reason why they won't assist. Ring their phone number to get the ball rolling. And then add the buyer to your blocked bidders list.