Apple India — IPhone 11 || Returned Dead

I purchased iPhone 11 128gb, black on 13th July 2020 after purchased Apple Extended Warranty Plan
It's just been two years and started facing issues.
When I went to the service center, in the diagnosis it was found that there was only mic issue and I told them battery was another issue so it will have to be sent to Bangalore service center.
The phone was in a working condition when I had given it to service center, but when my phone returned from the head office (Bangalore) the phone was dead and they detected unauthorized modification and internal damages. They gave me two options either to pay 40000 and get it replaced or return as it is.
So I asked them to return it as it is.
I even informed them I've never got my phone tested, cleaned or any other alterations done outside the service centre same has been confirmed by the B2X Service Solutions PVT LTD (Authorized Service Center from Apple)
Infact when I received my dead phone the service center also confirmed that the phone was sent to head office in a working condition and they haven't found any internal damage or unauthorized modification, they had a conversation with the apple chat support and mentioned the same to them. They even shared the pictures of the phone which were taken when I was leaving my phone at service center.
Later chat support stated that they were escalating this matter to the team it would get my issue resolved within 3 to 5 days. But nothing has happened till now.
This is very disappointing that a huge brand would do such a mistake, I'm suffering a lot as I'm working from home and my office meetings and calls are missing.