Contact ebay (best option is to request a callback via the help and contact link at the top of the page, they usually call back in a minute or two, but you might be on hold for a bit).

They will be able to access the buyer's messages, so if the buyer clearly indicated they damaged the item, the rep will be able to see that and will hopefully be able to assist (ideally, they'll close the case straight away in your favour, since the case was opened under false pretenses, but you might strike a rep who still thinks you have to do whatever the buyer wants - if so, ask to speak to someone else, eg a supervisor).