Xiaomi Redmi - Xiaomi India poor quality redmi note 7s

I have bought Redmi Note *s on *st of July **** which was delivered on *rd July ****. I started using from the *rd evening. When I charged the mobile on *th July **** I felt the temperature was very high. When the day passes the battery drained so fast. In the afternoon the battery went below **%. I was using honor *Lite previously which was too good in battery backup.
When I asked my friends who are all using Note * pro told the battery is **% even at * pm. I raised this complaint to MI support. After a week I got a response that too after many numbers of followups. I don't know whether MI support people know the meaning of escalation or not? Everyone told I have escalated your complaint. Still, the issue with my phone is not resolved. They have asked for a battery temperature screenshot for confirmation. i.e for product replacement.
Since I sent those screenshot on **th July **** they are telling that the product could not be replaced. Because the replacement policy is only ** days from the date of purchase. Why the back end team gave to call back on the *th of July. Why they did not give callback on *th July? They can give a call back after * days but now they are blaming me for sending the screenshot late? I need a proper reason for this.
First of all, they have sold the defective product. Why can't they accept that fact?