Xperia Z3 compact

My Xperia Z3 compact is 6 months old. I wanted to take pictures under water, after I checked all the covers to make sure that they are closed. After a minute or so the phone died and when I opened the covers it was wet inside. I took the phone to MTN and they said they could not repair it or could not help me since it was water damage. I am really disappointed since these phones are advertised as waterproof with warranty...