refused to void

On the 24 Feb 2016, I went to kfc, I was assisted by Mahlatsi my order was 50 rand zinger wings and another 8 zinger wings and street wise 3. After putting every thing i said on the till ,she then said I could have ordered 24 zinger wings and wise 3. I then said okay then place my order that way then. She bluntly refused saying she can not void. Why didnt she explain this to me as Customer before placing my order. She made me feel uncomfortable and that I placed my order incorrectly. She should have kept quiet and took the order like I said it. Poor service.