poor management

I bought a BlackBerry 9720 at CNA festival mall last year for R2500. 2 months ago the phone stopped charging and every time I take a pic the phone reboots. The phone has no liquid damage nor physical damages. I was called by their assistant manager and she said I must come to collect my phone. I then refused to collect my phone and I was told that the General manager would call me and instead he called me after 2 weeks. He then intern also said I must come and collect my phone as they could not fix the problem as I am the 1 that damaged the phone. I asked him what proof does he have that I damaged my phone he then said I must take it up with Vodacom as they did the assessment. He even try to make me take the blame on the faults of the phone. My phone is still under warranty. I am so upset that I no longer want my phone to be fixed but rather my full refund as the management of CNA have been unhelpful and rude. The BlackBerry 9720 has been discontinued due to it is a faulty phone and the General manager admitted that too. He then later changed his statement to that they just sell phones for Vodacom. Please help me out as CNA did not and won't. I work in retail too.