Wrong diagnose to the mulfunctioning new Nokia phonehone

I bought a Nokis phone at Checkers Hyper Menlyn, it has a problem of freezing and people not hearing me, I thought I was still learning to use it, I went back and told them but I didn't had a receipt with me they told me to bring it back, later they booked it in because now it was worse, it couldn't open when you switch on it only shows Android on the screen and never open the features, they booked it and later was contacted by the store to say they couldn't find a solution they referring it to MTN then later I was contacted to come take my phone that was not repaired. Reason being it is sim slot damaged, the store assistance was also surprised and we opened the slot it was still ohk, I tried to book it to another repairing supplier but they refused saying that problem is software related and they experienced that if they try to solve it it could damage the phone so they don't want it. I want to know how can the slim slot problem be realted to the software because if the slot was damaged it will open but not read the sim, but in this case it doesn't open it only shows the Android light and that is it. I want MTN to give me the technician that was giving that opinion and want to be refunded as the phone is still new and only used for less than four months when it start giving me the problem. I am now stuck with the phone in the box no crack no damage even today is still showing the same thing. My