Xiaomi India — Phone issue

I had purchased Mi 11 I in the month of July but ever since I started using, phone has hadany issues

The call volume is very low and we need to turn on speaker to hear during call
The call suddenly drops
The YouTube hangs when I fast forward videos.
The battery life is very low.
These problems started coming after 7 days of no replacement date and hence could not do anything. It cost me 28000 rs which is totally waste now