Of course you're entitled to a refund if the goods you purchased weren't "as described". (i.e. you didn't ask to buy an empty box, you asked to buy a game).
Assuming that the store is part of a chain, contact their head office and insist that they refund you or, if they initially refuse to do so, that they review their CCTV footage to show that you made a purchase in the store on that date.
Given that gaming stores shouldn't have been trading for the past few weeks though (unless, say, you're referring to the electronics section of a supermarket), it's hard to see how you made your purchase in the first place.