Fnb smart device

Fnb smart device wont replace my iphone 8 device even if its under warranty sighting water damage reasons, i cant be paying for a device that is broken. This device is only 8months old and i am left with the 12 installment on it. I want fnb smart device to rescind the debt or replace my device. I have been their loyal client for over a decade and in return they treat me like a nobody.