Bad service by game

So my sister bought an iPhone at Game Kokstad in August last year, the phone out of the blue went blank and wouldn't charge. She took it back to Game South Coast Mall and has been sent from pillar to post ever since with no help. They refuse to assist her but the phone is not even a year old. She now had to buy another phone because she needs it to be able to do her day to day functions.

They refuse to refund her or give her another phone, they told half truths and said they had taken the phone for repair but they had not.