Sony Xperia - Not so Waterproof

I purchased a Sony Xperia Z3 on my Vodacom contract-its advertised as being waterproof on TV so it suited my lifestyle perfectly.However, when the time came for me to use it underwater, not even 30cms deep, the phone got water in it.This was not the first time i had done so, so i knew to double check all the sealing points.I took the phone in to my local Vodacom,and well to cut a long story short they have told me that the phone is irreparable and it wont be replaced under warranty.When asked why,I get told that the 'water activation points' have been activated.The phone is advertised as water proof!! Then to further my questioning of the failure,when i initally took the phone to the repairs department, before i could even so much as mention the problem on the phone, the gentleman says 'let me guess, there has been water entry' further confirmation that mine is not the first! As mentioned before,this was not the first time that i had made use of the phone 'As Advertised' aswell as the gentleman comment at the help desk leads me to believe that this is a product failure and not that of my own.I expect the Service Provider - Vodacom - to come back to me with a more positive answer