non-acceptance of faulty goods

I did a renewal on my contract on 27 July at Vodacom Kimberley for a Samsung 6 Edge .After trying to install one social media app BBM the phone froze. I returned phone 28 July . As per procedure it needs to be assessed before can be replaced. I received a loan unit on 31 Jul as went out of country from 1-9 August. I went back to shop on 10 Aug & manager advised phone returned & they found no fault but phone still @ their local repair centre, will let me know when I can collect. I received call on Friday 14 Aug to collect phone. Manager gave me phone & advised they did a software update so phone sorted as they had phone on whole day and not freezing. Sunday 16 Aug tried again to install BBM, phone froze & heated up. Returned to store Monday 17 Aug. They sent me to repair centre to book in quicker. Called 24 Aug to follow-up with store manager, said I must follow-up directly with local repair centre. Went to centre Tue 25 Aug and manager said sent ph back as still heating up. Got call today 2 Sept from local repair centre advising that phone returned & no fault found....Why would I send a phone in twice....I need to follow-up all the time no accountability...frustrated