Incompetence and failed promises

I have a blackberry 9720 which keeps playing up. I have returned it 3 times now . The 2nd time i was given a reconditioned phone which I was unhappy about but had no choice.the the final time the technical department could find no fault and sent it back. It has gone to escalations who promised to call me on 2 occasions but never kept there word. Staff just kept repeating the same response that there was no fault. It is an inconsistant fault which means it can work fine for days and the it turns offby itself. This has been going on for a few weeks now. I finally collected the phone after getting nowhere with Vodacom staff. The phone worked for less than 1day and the same fault is still happening (of course, as it was not fixed or replaced) i asked at vodaworld 4 the phone to be changed to a diffefent make as this phone has caused ongoing problems. I cannot keep taking half a day off work to sit in a queue to keep getting the same make of phone back with little or no progress in fault finding.i have been a loyal customer for many years now, where is the loyalty of vodacom to its customers? We have choices.... what will you do to keep me as your customer. I need positive action.aviva