insufficien quality management

i bought a Samsung Phone at Markham Sandton on the 06/05/2015, few days later i discovered that the phone wasnt function well,hopely was a factory Tech faults.The device keeps restartingrebooting itself in a sudden way and mostly when i am on a calls.so 8 days later from the purchase date i went back to Sandton to return the phone and to expalin the reasons why.Tumelo(store manager) have said to me that they can't take the phone back as it has past the 7 days period and he advised that the matter is not Markham anymore i should take it up with network provider or Samsung.He then said the only option that they can do is to book the device for repairs which it will take 14 to 21 days.which i said i cannot afford to live that long without a phone because these is totaly not my fault the device is disfunctional.why must i be reffered to third parties bcoz i bought this from your store. i feel like my right as a customer were violated according to CPA acts and that Markham only care about taking my money. why must i suffer.i want Markham to take thier phone and credit my account or voucher.i'm not happy with the service and device only caused nothing but nighmare in my life.