Shocking service to a valued customer

Purchased a new iPhone 6S on 6 December 2015. On 7 January it switched itself off - could not turn it on. Took it in- sent for repairs. Got it back 15 January. Report : no problem found with the phone. On 20th January it switched off again. Booked in again Sunday 24th January - requested a new phone in terms of the CPA. 4th February - ready for collection. Same phone back with report : no problem found. I refused to take it. It was booked in again on the same day. Tuesday 16th February - ready for collection. Same phone - report: no problem found. Complained to the manager that this was unacceptable. Having owned the phone for 2.5 months, I have had the use of it for only 4 weeks. The manager said he would contact the Vodacom Apple rep and call me back within one hour. No call. 24 hours later I went back - he was out for the day! The deputy suggested it was a software problem. Whether hardware or software, Vodacom should have found the fault and fixed it. I am still without the use of the new phone, and no further offer of assistance from Vodacom.