Cashier attitude

I was buying groceries on Saturday, cashier helped me and I asked to withdraw cash with my purchase of R200. The lady gives me 2*R100 notes, and I asked her to give me 2* R50 notes to pay for parking. She said that she doesn't have, even though I could see from her drawer that she had several notes of R50, R20, and R10. I even told her that I can see the notes in her drawer, she still insisted that she does not have, and said to me she is keeping the notes to give change to other customers behind. The gentleman packing on the till realised our dispute and took my note to the cashier next till, and I got the change. The lady helping me continued with her business with no care in the world.