SONY XPERIA Z3 SUPPOSED TO BE WATERPROOF

My son's brand new cell phone, a Sony XPERIA Z3 stopped working after 5 days. We booked it into Altech Autopage in Hillcrest. Three weeks later it came back from their repair centre, with the message that it could not be repaired due to water damage. This phone is supposed to be WATERPROOF, NOT WATER RESISTANT, as per Sony's TV advert, and the adverts in Altech Autopage's glossy brochures. My son did NOT leave the ports on the phone open