Waterproof Sony Xperia Z3

My Sony Xperia Z3 fell in water a few weeks ago.All ports were closed but it got steam in the screen. It was not in the water for 30 minutes and it did not fall for over 1.5 meters in the water as the specifications say. I took it to MTN because it is a contract phone.They took it in and weeks later when I followed up I was told my phone is beyond economic repair and I should contact SONY and find their nearest branch. I called Sony service centre and the woman told me they don\t do third opinions and if MTN says it's beyond repair, it's beyond repair and there is nothing they can do. They referred me to their call centre. I called the Sony call centre and the man told me they cant help me.I told him when they advertised the phone they said it's waterproof ,so what am I supposed to do now? They blatantly told me there is nothing they can do.Please help me Peter,this is false advertising."