Bad customer service

I received a bad customer service at Truworths Jabulani Mall. I went I to the store to exchange dresses that where given to us as a present. I didn't want a cash refund but wanted to exchange the sizes. I told the lady(manager) that I received the dresses a presents for my daughters and I would like to exchange the sizes then she told me that she won't exchange them for me since I don't have an invoice. The problem is the person who gifted us with the dress is out of the country and by the time she comes back the 30 Days policy would have passed.