Failure to repair phone, failure to replace phone

I purchased a Sony Xperia Z3 - at the time the top-of-the-range phone. It has a 1 year warranty. It is waterproof, and the back cover cannot come off.<br> <br> I brought the phone back to the Randburg MTN service centre on the 9th August 2015 as it had moisture in the camera.<br> <br> On the 17th of August I received an SMS to collect my phone - off I go and the phone is in EXACTLY the same state. Nothing at all was done, and I had to book it in immediately again.<br> <br> On the 27th of August I received another SMS to collect my phone - this time the back cover was changed, no moisture. Good.<br> <br> Almost immediately, however, moisture crept in and it eventually made the camera unusable in November. I could only book it in on 9th of December. This is now the THIRD time the phone has been booked in for EXACTLY the same reason. It took until today, the 7th of January for me to receive an SMS to collect my device. In emails with the store manager he said the phone had been replaced by Sony.<br> <br> So off I go again, for the 4th time, only to be given a phone with EXACTLY the same problem (moisture in the camera lens). This is now the FOURTH time the phone is back, for the same reason.<br> <br> The phone is under warranty.