Not refunding broken mobile phone

Bought a mobile phone from Edgar's Active at Tygervalley Cape Town. The phone was faulty and they replaced the phone. I received no report from the workshop as to what was actually wrong with the phone. The second phone showed the same problem. I also took this phone back and immediately purchases a more expensive phone since I could not wait another 5 week to have a phone replaced. I made it clear that I would like my money back since the original model phone kept on failing and that I honored the 6 month guarantee period. After 5 weeks I was informed that 3 third phone (of the same model that kept on failing) is ready for my collection at the store. And they refuse to pay back my money.