Cell C Selling faulty phones (Sony M4 Aqua)

I need a new phone to be sent to me, I went to the cell c store in Randfontein to report that my Sony M4 Aqua is faulty again. in the 2 and half months that I have had to book it in at Northgate mall for repairs and now it is switching off again and doesnt move past the Sony welcome window angain and the store at Randfontein wants to book it in for another repair session. this is highly unacceptable and bad service from both these companies. I cannot pay for a phone that will constantly die anytime it wasnts to.