Brand new phone is unpreparable.

I've purchased the Sony Xperia z3 compact on contract, on the 05/12/2014. Only because I needed a phone that's battery life can last and it's waterproof, besides that the phone fell and was sent for repairs on the 29/12/2014 the job card number was ctwic***. I've paid for the phone to be fix at R3958.90 and the date I received it was 14/02/2015. Say 3 months down the line the phones battery life wasn't lasting like it use to be, I have notice that the battery also began swelling, A brand new battery does not do this in such a short period of time. Soon after the phone has not been switching on also. I took my phone back into repairs at the same place Mtn HVRC Cape town, the date that I booked the phone in was on the 29/07/2015 Job number ***. Received a sms saying I can come fetch my phone. They stated that the phone is beyond economical repair, because of water damage on the board. My phone has not been near or even close to water. The battery that was place in that phone was a second hand battery because it leaked onto the board.<br> <br> I have been a loyal customer to mtn, but this is unacceptable and I will close my contract without paying the monthly fee!!<br>