Altech autopage vs CPA

I went to upgrade my contract at Altech Autopage on 12 February 2015. I visited their Ballito branch and received my new Xperia Z3 on the same day. The cellphone worked fine until 27th February 2015, when I noticed the bottom of the screen lighting up and fading continously with alot of lines running across the screen. As soon as I noticed this I tried to call the Ballito branch to inform them of what was happening to my phone, but on several attempts there was no answer. I visited their store on Saturday, 28th February 2015, and showed the consultant the phone to which she rep****, the was a problem with the lcd screen. I told her that I would like to have the phone replaced as it was only 15 days old. She rep**** that they could not replace the phone and that it would have to be sent to their repair department to assessed before they could decide whether it would be repaired or replaced. I asked if they would give me a courtesy phone to use but was told they don't offer that. She also told me they won't replace the phone as they have a 7 day CPA. I called their customer service only to get the same response from 2 agents. What about the National CPA and my rights?