Xiaomi India — screen cracked during charging

I kept my phone for charging. While charging screen of my redmi note 4 phone got cracked. My phone is under warranty. Person of the service center and from call center of mi say its a physical damage and you have to pay for it. But how it is a physical damage, the screen automatically cracked while charging. Persons from service center are asking money to diagnose a problem. The phone is under warranty then why do i pay for the same. It's not my mistake. They said it never happened before either phone burns but the screen never cracks. But this happened with my phone in front of me but no one is listening to me. It never happened before that doesn't mean it won't happen.
So whats next, as i am not ready to pay, the phone is under warranty. What is the solution?