Sick & tired.... 4th repair - same response!!!!

I actually do not know where to begin. Today I collected my phone (Sony Xperia M2) from Vodacom repairs Alberton after taking it in for the fourth time for the same problem. The screen on my xperia goes blank and I am unable to turn the device on. The last problem was that the screen froze and I was unable to turn the phone on or off. this is after only having my phone back for two days. always get the same response.., No fault found and a software update was done. I reported this to Sony Customer Care... What a waste, Sean Gibbons has tried to assist and escalated my problem to no avail. I have been a Vodacom customer for more than ten years and I am ready to move my business else where. What do I need to do to get a replacement unit? How many more times must I take my phone in for the same problem? Who do I have to complain to to get an answer? Where are the decision makers? Why is Vodacom not taking a stand against Sony and insisting on a new device? Why do I have to complain on HelloPeter.com to get any kind of response? I have all the job cards and all the dispatch notes.. Same answer each time. I'm now sick and tired of being inconvenienced...