Bad service from Cosave Powerbuild because of colour of my skin

I went to a shop to buy a paint at Cosave Powerbuild at Hercules and gave the salesman a colour of a paint I want for the Wall. He then mixed it for me. This morning when the my painter open the tins he found that it is enamel instead of PVA. I went to the shop for exchange. The cashier called the manager in charge. He was very rude to me and he refused to exchange the 2 tins of 5 litre of paint (Stevens) @ R1090. I'm very frustrated cause I don't know what to do with it. I'm am told this is how they treat black people in store. But they exchange things for White without guestion