Lumia phone keeps shutting down

My 1320 Lumia keeps shutting down even after I hard reset the device to factory default settings. This has been happening since I received the device from Vodacom a few months ago and is highly annoying. I took the device in for repairs with Vodacom but the same still happens within an hour of starting to use the phone (shutdown twice!). This phone had this problem since the day I received it but the frequency of the problem has increased to a point where I can no longer use the phone. This Lumia is damaged goods.<br>