REFUND REFUSAL AT CASH CRUSADERS

Greetings...I type this with such huge heartbreak. I bought a laptop yesterday at Cash Crusaders in Newtown Johannesburg and I just brought it back today as it doesn't work and I am a student who used her last money to buy it. The manager and the sales person called Laz there are both refusing to refund me whereas the slip at the back is written that I can either exchange the laptop or get a refund. I've been sitting here ignored for two hours now as they do not want to refund me my money. Please assist on how I can go about with this.