I have a freezing problem with my phone

I upgraded in December 2015 and since then I've never enjoyed it. My new phone was exchanged the first time I took it in for software upgrade and was never informed this was in January and was informed by my insurance when I lodge my complaint with them sometime last month with no option left I thought the insurance will be my saviour. I had been given three refurbished phones within 6 months and the recent one which I got last Thursday its starting to freeze I must say I'm totally not happy with the service I'm receiving from Vodacare especially when they exchanged my new phone and not informing me. I had just made a first payment for it . I've had it from driving to and from Cresta branch every month. Last month when I took it in with same problem the employee there calculated the times.I've visited and it was the seventh time. I dont take a week with their new phone to start experience this freezing problem. Its a contiuous problem. I'm asking for your help cos I've no other option.