Refused to exchange for a gift card

I purchased items cash from Foschini (SodaBloc) for my daughter and misplaced the slip. When I needed to return the items as they didn't fit well and requested a gift voucher, the SodaBloc assistant at The Pavilion advised she cannot assist me because I don't have the cash receipt and it doesn't matter that I wanted a gift card in exchange. This is also despite the fact that the cashiers always request for your I.D number whenever you purchase something from Foschini for their 'rewards programme'.