Sony Xperia M4 Aqua

Today is now the third time that I have had to take my Sony Xpeia M4 Aqua ( D2304)to the Vodacom repair shop because my screen keeps going blank and the handset wont switch on. The second time was within 2 days of receiving it back from the first repair. I now want a replacement unit. Each time the handset goes blank I am inconvenienced. I requested a replacement unit when I took it in the second time and I received the same handset back. If it is faulty why not just replace it. Why cause the customer such an inconvenience each time. Fighting with Vodacom repairs does not help because they say that Sony needs to make that decision to replace the handset and a complaint on hello peter will help escalate my complaint. why does one have to complain first???