I went in to buy a expansion pack for the DC build...

I went in to buy a expansion pack for the DC building card game for my uncles bday present, it turns out he already had those cards so I went in to tell the lady, (whom btw sold me the expansion pack) what happened I told I do not have a receipt but I would gladly take a store credit, she said it is not in a sale-able condition thus she cannot take it. Really? I had it in my backpack for 2 weeks with nothing in it, it hasn't been open so tell how can it not be saleable?? I was playing to use the store credit to buy the other DC teen titans game but you lost my business.