WHO AT VODACOM CAN MAKE THE CALL?

I have a Sony Xperia M2 Aqua. I have taken it to Vodacom repairs a total of 7 times in less than a year with an interval space of between 2 weeks and 6 weeks. Each time i have the same problem, the screen will go blank or it switches off randomly and wont charge. I get the same lip service each time i take my phone in and that is that it will be escalated and the manager would personally request a replacement phone from the supplier SONY. Each time i receive my faulty phone back with a note on it that no fault was found. Surely if one phone has to be repaired 7 times in less than a year there must be a problem. When i collected my phone after the last repair less than 2 weeks ago i was told to call vodacom repairs on ***.. No luck, then customer care on 082 111 who promptly put me through to the upgrade centre telling me that they would be able to replace my unit.. Well. It turns out that because i didn't to my upgrade telephonically or online nothing can be done about it and i must go to the Vodacom store where i did my upgrade. I was quite upset and insisted on a managers number but was told there was no one available. Where does one go from here? Who at VODACOM can assist??