Iphone XS is not water resistant

My iPhone Xs just bought it last year in July! For some reason when I plugged my charge into my phone, the phone went black screen. I chatted with the agent and followed his instructions and reset my phone but still black screen and I lost all of the data.

Then I mailed my phone for repair. At first, Apple told me it was broken because of liquid damage. Ok, I knew it is water-resistant there were only water spills on the phone. I did not drop it into the water, also I bought it because it advertised can be used underwater for 30 minutes then how can water spills cause my phone to die? Then later, the support team told me another thi! They say they noticed it shows signs of accidental damage or misuse. So what is the really cause of black scree? The scratches on my phone was caused long ago, so the blackscreen cannot be caused by accidental danage. I just want to know what cause it!