3rd time phone went in for repair

I had an windows phone its 4months old ,and it went in for 3rd repair,and everytime it has the same problem I also notice that it switch on and off by himself when it came back,yesterday I went to americans swiss sanlam centre they phone to listen haw far is the phone I wanted to speak to the lady but she refused ,I ones spoke to manager at american swiss she told me to bring the phone back and when its going in for 3rd time they must replace if there is stock,she no longer working there what must I know do coz I paid 1000rand cash and 300 I took on my account ,I'm a loser now,why can't they reaplace or refund my cash,for two months I'm not using my phone due to its sitting in JHB for repair