New pone has signal problems

In February I got a new blackberry 9720. Two weeks after using the phone, it started having network problem. I went to vodacom repair centre more than one time but they cannot detect the problem of the phone. I even received a call from a technician at advanced repair centre and he even stated that since the phone is new, should they not be able to detect the problem a new phone needs to be issues to me. I have assessing the extent of the problem up to date. At time the phone can be on SOS for more than 30minutes, I get missed calls while my phone is off. The consumer protect said should try to resolve this first should I fail, they will intervene. <br> Can anyone intervene be issued with a new phone.<br>