Apple India — Sold me a defective Iphone

I had complained several times in apple service centre and apple support but they are not helping me. My phone's battery health had decreased to 91% in less than 20 days. The service center had acknowledged that Iphone 11 has battery problems but still they are not resolving my complaint. They are misguiding me and asking for service charge as well even my Iphone is under warranty. My IPhone 11 is 6 months old i had made the first complaint on 13th August 2021 regarding the battery health but got no response. They run the diagnosis and said that there is no issue found they are not listening to my complaints and apple doesn't have any complaint email or contact department. I have visited the apple service center today and they said thay yes in Iphone 11 this issue is very common and instead of doing something about it they told me that they can not do anything. It means that apple is aware that there device are defective and they dont want to repair them. Apple had sold me a defective product they are fraud and looted my money. I want a resolution.