liquid got into the phone

hello. I have a problem: the phone (iPhone 12) stopped reading the sim card. The re:Store service center told me that there are traces of water in the phone. I have had my iPhone for less than a year and it has already been repaired under warranty. Now the service center refused to repair under warranty, offered a complete replacement of the device for my money. I didn't put my iPhone in water. I don't know how the water got there. Are you going to do something about this situation? You tell about waterproof in your iPhone, but it's not.