Sony Xperia M2 Aqua

My name is Frederik Bester Louw. I took out a contract with Vodacom at the end of January 2015. The phone started to give problems, so they send it away for repair. Not even a month after that the phone gave the same problem as the first time, after the 3rd party repaired it. So I book it in again ant requested a new phone. It went back to Sony and they send it back and said they dont find the problem and that phone is fine. A week after I got the phone back it gave the same problem again. My wife took a video of the problem for proof. I ask vodacom again for new phone and they said i must book phone in again, because they can just gave a new phone it first must go to 3rd party. I booked it in again and know i got a sms that say \Job number ***1is in transit to vodacom tygervallay". I called them and they said that Sony says there is nothing wrong with the phone after i have proof. So for a month and a half i paid for a phone that i didnt had. What is there to do because i dont want the phone back and i not gonna pay them a cent further. I want to cancel the debit order at bank. """