Cellphone repairs

I bought a Samsung Trend Neo phone - IMEI No ***, from Edgars Carnival Mall on 15 March 2015. the phone works for a week or 2, then the system seems to hang, I cannot receive calls, make calls, send messages unless the phone is re-booted or in some instances, I need to remove the battery and then the phone works again. Since the time I bought the phone, it had to be sent in for repairs 3 times, first time on 29/4/205 - job number ***3, which was 'repaired' by updating the software, how is this possible, a new phone?? On 19/6/205, on job number ***4, the phone needed to be sent back for 'repairs' as it had the same problem. This time when the phone came back, I was told it is the battery that was the problem, how that was determined, I don't know, as I the store took the original battery out and gave it to me, when the phone was booked in. On 17/7/2015 the phone went back again, for the same issue, this time when the phone came back I was told the technician could not find anything wrong. Why will no one take responsibility and give me a phone that works?? Edgars says it is a call for Vodacom to make, Vodacom says it is Edgars, and I am left with no phone!!!!