sony z2. water damage

Good day, I had purchased a sony Z2. Lastyear August from vodacom chatsworth, in may this year I went on holiday n I decided to take a unwderwater picture, wen I woke I came out of the pool my fone was frozen and didn't want to work , I did all da procedures before going underwater making sure the flaps was closed , wen I gave it for repairs vodacom tells me they can't sort it out because its a water damage, how can a waterproof fone get water damaged ? Sony can be brought up for false advertising