The best option would be cancel the listing, citing "Problem With Buyer's Address" as the reason why so as to avoid eBay hitting you with a defect. You can then relist the item for sale again, although if you choose to do so then considering the fact that the buyer has failed to respond to any of your messages I would advise you to add the buyer's User ID to your Blocked Bidders List and wait for a period of at least forty-eight hours for the blocks to kick in and take effect. The blocks would have kicked in straightaway had you never entered into a transaction with this person, but that's not the case with recent buyers, hence the reason why you need to wait at least forty-eight hours if you decide to block the buyer and then relist the item.
After at least forty-eight hours have passed since the point at which you added the buyer's User ID to your Blocked Bidders List you can then relist the item for sale again, as that way the blocks will have kicked in, thus preventing the original buyer from being able to purchase the item a second time and causing you the same problems that prompted you to start this thread in the first place.
