NEW PHONE BUT FOUND IT WAS ALREADY ACTIVATED

I bought my phone on 24 December 2013 with IMEI ***, the phone started freezing MTN told me to get a new SIM card. I did it still froze. When I went back they said I need a software update on my phone. When I took the phone to The Manager Chantel Clearwater Mall MTN told me that my phone is out of warranty and that the phone was activated on someone else's name in September 2012 on a top-up contract (Proof was sent to me). I have lodged a complain with MTN AREND MALL BRITS but Geraldine just don't return my calls or emails or sms. I had to pay R2500 cash for a phone that is actually used. I have lodged so many complains on HelloPeter for MTN but they just not make any plan to help me sort this out. It's really unacceptable because it is as good as *****. Please if you buy a phone at the MTN Arend Mall, make sure it has not been activated or used before as they sell activated phones in boxes as new. I now have a phone that is more than two years old and according to me a year and a few months. I know now why they sold it for cash and not on the system.