Bad Customer Service

I have recently bought a Apple MacBook from FNB. On delivery of my MacBook the device powered on, but later powered off again and wouldn't power back on. I booked it in at the iStore in Cresta within 7 working days, and according to my knowledge if your device is sent back within this period of time they need to send you a replacement. They never did. Sent me the same device a week later and within hours of having it back, the same thing happened. They told me this matter will be resolved within 3-4 working days, it's been 5 working days now and I have yet received feedback. The customer service is poor, and their turnover time slow. They refuse to send me a replacement device even after all the right procedures were followed from my side. I cannot pay such a big amount of money on a device and then after having it for a few hours be refused my customer rights.