Xiaomi India — mi note 6 pro bulges battery problem

Address:

Kurpania near chaiti durga mandap, Kurpania, Bokaro, Jharkhand, 829127

Hello, I'm Rahul Kumar from bokaro, jharkhand. Me buy my new mi note 6 pro in the month of January 2019, but after 2-3 months my phone battery getting drained very fast and doesn't give me backup, so i take it to Xiaomi(annapurna service) care which is situated in ranchi, after checking my phone, they said to me that sir you have to give a some of 1356 Rs. Because your battery is licked and it have some physical damage(but I'm never opened it before in any local service center), after hearing that I surprised because my phone is in warranty, then why they charged me. After discussing they didn't change my phone battery after I paid the Bill then they repair my phone. So please justice my problem.