Truenet Commerce — redmi note 5 pro from flipkart

I have ordered redmi note 5 pro from flipkart and the seller is truenet commerce. After receiving i have been using the mobile for 3 months and suddenly it got switched off while using and not able to turn on again. Then i took it to mi service centre located in guduvanchery chennai, after checking the mobile they said that the mobile was already opened somewhere else. But i never given this mobile this to anywhere and this is my first probelm and i am going directly to mi service centre.. Then i have complained to mi customer care they have no option to accept this issue and i complained in flipkart now they are telling like we will check with seller.. I thought the seller is responsible for this issue. So please check the seller truenet commerce.. I can see lot of complaints against this seller but flipkart gave them for 4.9 ratings. Even this is flipkart assured product no one is ready to accept this problem. Kindly take action on this..