I was denied service because I commented on the slowness of that day's service

On Sunday I went to Checkers in Sunnypark, Pretoria to buy my groceries. After waiting in a que for more than 15 min, the cashier with a name tag written Obakeng Phiri, over head me talking with another customer about how slow the service was that day. She the called another worker there Molebo Mokoena and told her that I am a problem. She then looked at me and said "i'll show you". She started working even slower and calling other collegues, including her supervisor who wasn't wearing a ne tag to show them me. When it was my turn to pay she said the systerm is nolonger working and laughed with her collegues. I asked what am I supposed to do, she said I should go to a faster shop. I had no choice but to leave cause when I asked for manager she called one of the collegues she was busy showing me to.