Replacement/ repair service

Bought an Iphone 5 S cash at Istore Sandton after a 2 months had problems with the the white line as an LCD issue, Took the iphone to mall of Africa and the sent the phone to Core Group Repair centre on behlf of Iphone. they had issue saying the phone was bought in 2015, whilst I sent POP dated August 2017. The matter has been with them for 3 weeks after numerous follow ups. then I received the new replacement device on the 2nd Nov 2017 after a few hours the issue with the new phone agin and now when I call today this morning I was promised a return call with the service manager, still waiting no call back when i called back at 14:30 no pick up. I neeed to get my money back and upgrade to another model phone or get a new phone with no delays again for 3-4 weeks