unreliable source and peutrit customer service

My Sony Z2 started giving me problem. I contacted the SONY support centre, they arranged for my device to be collected via courier. After 2weeks I contact them, only to be informed that it will cost me R4150 to have my device fixed as it has water damage and LCD cracked. When I sent the phone away I had no problem with the screen at all. The phone just heated up and it selected pictures and apps, to me it seemed more of a software problem. I contacted SONY support centre as I am unhappy to pay this amount as my phone is only 5months old and to my knowledge the phone is water proof. After exposing the phone to water once the phone worked perfect. Due to these findings my warranty has also now been ceased. SONY mobile response was that there is nothing the can do for me.