Voucher for shoe on sale

Went to the outside Randburg store. The one outside of the mall. I had bought shoes for my sister, It is her size however there are abit tight, I asked the lady if I could get a voucher that way my sister. She refused, she said you guys don't offer vouchers. Now I had to walk around looking for something else, which I did not find. I had to take the shoes with me, I still haven't changed the shoes as we speak. I don't get why you guys don't give out vouchers for a sale item. Why???