Faulty new phone

My new phone went in for repairs 3 times in less than 4 months and I reported it faulty again but could not bring it in as I was out of town. Each time it was the microphone that went silent. Then suddenly the screen went off, but I could receive calls, even when I cant hear the caller. When I took the phone in, the consultant started pressing the screen but took it to the technical div where I could not see them. 15 min later she returns and accuses me of having removed the memory card and sim card to which I said, I have no idea on how to install or remove it as these were now missing. I was made to feel like a **** and after 10min of arguing, I told her to look at the back where she had taken the phone. She then comes back with the sim card and told me the screen had a crack, which I never saw before. I would not carry a crack screen/glass in my handbag because it could shatter further and leave glass all over. I was quoted R2400, but I am not prepared to take back a phone which were new in October'15 and faulty to begin with and is in a worse state now with a cracked screen. Nobody there wants to take responsibility and say it is all my fault because the screen is cracked.