Iphone problem and they wont replace it

So i recently bought an iPhone 6s a couple of weeks ago. All of a sudden while i was using it (whatsapp), the phone screen went immediately blank and the phone was dead. I tried to turn the phone on and it just refused to. I gave up from pressing the home and power button so i decided to give it a "hard reset", i held the buttons for a while but nothing happened. i simply gave up. as soon as i got home i plugged it into the charger, nothing. so i took it down to the shop i bought it from(Starlink) and asked for a replacement, i mean... its brand new, no scratches, never dropped it, it was working perfectly.. so they said they will take it in for a "check". so they sent me an sms 2 days later and told me to visit them,so i did. when i got to the shop they told me they opened my phone up and they told me its "water damaged" , the problem is i never spilled anything on my phone, it rarely rains in my country(Qatar) and im certain no liquid ever touched the phone. And i did talk to them about it, So my phone just randomly busted out although it was not my fault. i told them i had a warranty but they said it wont cover it. Now I am stuck with no phone. I used to own samsung for 5 years and always had to upgrade it to the newer version, and i had 0 problems using their products. but i decided i would try a new thing... IPHONE 6S!!!!! ... 2 weeks later... dead. and i cant do anything about it now. the reseller wont replace it or do anything about it .. 860$ gone to waste. Thanks apple. Much regrets.