Flipkart - Defected Redmi note 7 pro Flipkart not returning

I bought Redmi Note * Pro from Flipkart specifically to shoot videos. Right out of the box the camera showed a major lag in when a video is shot. There are frame drops and it feels like the phone is hanging. I called MI and Flipkart. Mi told me to update which I already had done. Updating did not work at all. The video lag issue got worse. MI told me to get the phone replaced by Flipkart.
So on the day of delivery, I initiated a return. Flipkart arranged a technician visit. It was mental harassing, to say the least. I shot a video in front of him which showed clear lag and he did not acknowledge saying that it is not a DSLR! It was really frustrating. After he went away, I get a message that my return has been cancelled.
Then I call Flipkart, they say that they will investigate the matter. It took them a total of * days to do that (notice that I only get ** days of window to return). Then one more technician visit was arranged and this time he agreed that there indeed was a serious camera video lag. He called his senior and that senior told him that this problem is with every redmi note * Pro and that Mi will provide a software update (I've checked the forums and this problem hasn't been solved since two months now and I have no hope in Mi that they will solve it now).
I ask this second technician to report what he witnessed and he was nice, he said he will report about the lag. But again I get an email that my return has been cancelled. This is too harassing for a customer. I am posting a video I took while with the first technician.