Iphone warranty

So I bought a brand new iphone Xs max three months ago and I was happy with it especially the water proof feature. Last holiday i went on vacation to relax and enjoy nature and take some photos and videos With my powerful iphone camera. Dramatically after enjoying some rafting time in the river with my iphone inside my trousers pocket trusting the water proof ip68 feature i was shocked when that water proof feature didn’t protect my iPhone from my wet clothes. It didnt even go under water or directly touch water. Apparently water reached the inside of my phone and did damage to it, the volume and power buttons are not working properly and there is a vertical line on my screen. So i didn’t hesitate contacting the seller and after inspection it they told me that water is the cause of the damage and isn’t covered by the warranty. I was shocked and felt betrayed, How is it possible for an ip68 water proof phone not being able to keep water out and then telling me is not covered by the warranty. On the other hand I have two friends with Samsung Galaxy S 8 and Galaxy S 10 phones and they never have trouble using their phones around water and sometimes they go under water in the swimming pool with no trouble. Well, I need someone to explain to me the ip68 feature and why it isn’t working with water plus it isn’t covered by warranty. Thank you