Xiaomi India — Phone is hang and do not work properly

I have buy mi note 4g on 16 august and have complaint in 3rd day, i go to airtel customer care they said to update my phone but after update there is little problem after update at that tie they have to replace my phone that they say in 10 day any problem occur they will replace my phone but they not replace it. after 6 day there is any problem occuring my phone hang when someone calls and not detectin my sim card, now i have given my phone to repair at airtel customer care. now i request you to replace my phone