I would just cancel the transaction and refund them completely through paypal. Obviously, something is up with that person that they would open a case on an item they don't even have unless they bought two from two separate sellers and got confused or something. You could try writing them and asking them why they opened a case on an item they didn't have yet. Are you slow to ship it? This is so weird. I guess I will never be surprised at ehat can come up with buyers these days. Maybe they changed their mind and don't want the item after all. This is a new one.