Bad business service

I bought Sub pcba for A04e for R150 and ask for a slip just incase I need to bring it back. They don't give slip, it happens the new sub pcba is still doing the same fault as the old one so it means the fault is on the main board so I return it. They are 5 Indian guys there and their faces it's not important I wanted a product, now they want me to point who I bought it from and I told them I don't remember the face cos I ask for a slip and there is a stamp on their sub pcba. Then they dispute that they charged R150 and they say the sub pcba is R50. We argue then when I say give me that R50 is fine now they say they not doing refund and I told them I want to exchange for a screen. Now they say they don't do exchange. Now I have to go back home with that sub pcba. It's not about the R150 it's how they treat people, specially blacks so I wanted to be even physical cos they even gang up on me.