Worst Customer service, Engen Gateway

Received the worst customer service ever at an Engen garage in Gateway Centurion. Walked in this morning before 10am to buy 2 red bulls of different sizes, to find a bigger one (500ml) was R13.50 on the price label. When I got to the till, I'm told the big one is about R30. I then told the cashier that's not the price I saw. He called the manager Angie Dube that took forever to come and assist because she was still on the phone. Eventually She comes and says straight to my face, she will not change the price as it was not meant to be where I saw it. She did not even apologize for an incorrect pricing. She went into an argument with me, shouting repeating that she won't change the price. She just left me by the counter standing after a long argument. I'd really appreciate if the lady would apologize to me as she had the nerve to shout and still honor me the price.