Could not exchange a gift

I went to the Cradlestone branch to exchange a dress my mother bought for me on her account. At first the lady was very helpful to exchange my dress for me. We went through the whole process of the exchange. Only afterwards she told me I needed the account card to complete the exchange. Because the dress was a gift I only had the slip with me. So I was told in that case they won't be able to assist me any further. If this was explained to me before hand I would have known and would have taken the initial dress back home. Now I had to leave without anything. The supervisor made me feel like I should have known how the system works. I do not work for TFG, I do not know the internal processes. It would just be nice if the employees can explain that to customers before hand without making us feel stupid.