water damage

I have a sony z2 .I use to take pictures under water of my fish tank. Everything was working on the phone but after about 10 months the phone started to give hardware and software problems so I took it into vodacom and they repaired my phone with new hardware and software and the phone was working fine when I got it back. About three weeks after I got my new phone back I decided to take pictures of my fish tank with the new and improved phone that vodacom gave back to me. After I took the photo under water my phone started to get go white and the picture dissapeared. I told vodacom I never had a problem taking pictures under water with the first original phone I bought from them but now this phone that vodacom recently gave back to me all of a sudden got water damage. They sent it in for repairs and when it came back they said it's beyond repairs and they cnt issue me a new phone even if its a waterproof phone and even if i still have a warranty on the phone. They gave the phone back to me and told me I must go to sony myself and sort it out. But the thing is I bought the phone from vodacom and still paying R500 a month for a phone that is broken.i am really dissapointed in vodacom