Cell C fail

Over 6 months ago my contracted iphone5c would often not ring and go straight to voicemail. This was along with the endless call fails. I first took it to the Canal walk branch where they said they fixed it but didn't. Then I took it to Claremont branch, same thing. All the guys there thought they could fix it in the settings. I knew this not to be the case as I had googled it and it was a common problem with the phone. I had had enough and thru a hellopeter post a call centre guy called me. He said the tygervalley branch had courtesy phones and I could get one. Finally i thought, here was someone who could help. No. Once I got to the branch there was no phone I could use.The guy then tried to change the settings and told me that would work. It didn't. So i took my phone in and was told that it was still under warranty. Cell C's response is that I must pay R5756.28 for a new phone because it is just over two weeks out of warranty. This is their decision after I had spent many hours of time wasted and extra costs by having to call people back. Why didn't anyone ever make the correct decision regarding this phone ? How do they expect to keep customers like this .