Selling Used Parts & Worst Customer Service

I bought parts from Goldwagen Randpark Ridge and I received Worst service ever. I bought parts for my car, and upon trying to install them I realised that they were used parts, not brand new as i had paid for. I informed the Manager by the name of Musa immediately, who advised me that he would get back to me. He did not. 4 days later I made a follow up, to which I was being put on-hold throughout the day until afternoon when he eventually phoned me back. I sent him images of the parts, receipts, boxes etc, and he acknowledged that the parts were indeed used and that it was a mistake from their side. I told him I needed a refund, and he offered me R200 out of the R1500 that I paid. That was his definition of helping me, and he was actually rude about it. I was so disgusted and insulted by this service.