Being ****** change

Spar Mams Mall cashiers keeps on robbing me of change. Today i got charged bread on my slip, to my suprise i did not buy bread. As a result my change was short and i only realised when i wet through my slip just outside the shop. This is not something new, it happened a few month ago but i let it slip. Apparently when you buy plastic, cashier's have a tendency of hitting the code of white bread which cost R10 instead of the carry bag requested. It may seem as a small amount but R10 is a lot of money. What angered me the most was the of the attitude cashier when i made her aware of this. No apology of some sorts. She just requested me to leave her the slip by force. If this how customer service is defined in the 31st century?