Extremely Bad Customer Service at Cash Crusaders Mall at 55 in Centurion

Cash Crusaders Mall @ 55 near Forest Hill city. I bought a lap top 2 weeks ago. I couldn't use it because the password of the previous owner was still there. I took it back and only got it back 3 days ago. That's when I discovered that the speed was very slow. I returned it and requested to add money and get a faster one. The manager refused to upgrade for me irrespective of me paying the difference. Instead he insisted I should resell it to him for R1500, whereas I bought it for R2400. He insisted they needed to make more profit on the same laptop I had for 3 days and never used it. I resold it to them for R1500 which means I lost R900 in the whole transaction. The manager was very rude and desperately willing to rob me which he did.