Amazon India — MI mobile not repair even on warranty

Address:

Rajajinagar

I have purchased mobile in Amazon and used for 7months and suddenly after update my speaker stopped working. I went to mi service center and showed my mobile and they took, after some time the store person called me and said it's out of warranty then I said I have the bill of warranty.
Then he said the mobile is already in opend state so they won't claim warranty.

I don't understand when I have warranty on my phone then why should I give my mobile to private service center and waste my money.

When I argue on this they said to speak with customer care. And I called them.
Then they said I have to change mother board and display.
It will cost Rs 4200.
Where mobile cost is only Rs 7000.

Please see how it's going on
when I gave my mobile everything was fine only speaker issue was there now they are saying I have to get changed mother board and display.

I need a fast response.

I am filing a complaint against Amazon and als against MI service center.

Still I have not collected my mobile.

Please read my concern and solve the issue or I will do as what I have mentioned above

Thank you.