every 3 months my phone keeps switching off

I have a Blackberry 9720 on contract with Vodacom. Every 3 months the phone will start to switch itself off. I have sent to Vodacom for repairs for the 3rd time and all they did is to upgrade the software, they did not even change the battery. I was told that the phone was sent to technicians and they opened it, my camera has something that is blocking it on the inside, for people that opened it they would have pushed it back so that the camera is visible, but clearly the phone was not even opened. I met someone that works at Vodacom who told me that the policy says that after sending the phone for repairs with the same problem 3 times they are supposed to give me a new one.I called and was told that there is nothing wrong with my phone. I am perplexed at this kind of service to say the least. Contract phone means they gain, how about the service goes with the gaining because I will give them this phone next time it starts its switching off stunts and then they can bill me and keep their useless device, I really do not have the time to go there until my contract expires, that's what they waiting for.