Apple Inc - Defective product received when asked for replacement they re not replacing the product

I bought an iPhone ** on Flipkart on October *, ****. After using it for ** days, it automatically switched off then I went to apple service center, they did primary tests on it and told Mother Board of the product is not working, they told it's under warranty period, you'll get the resolution as per your expectations (I told them that I want complete new sealed product as it's with manufacturing defects), So I submitted my iPhone ** there, after going through services they had now they're saying that your iPhone ** rear part is completely changed only your old display is not changed rest changed. I told them I want new sealed product only, they said we won't give you a new product you have to accept it. Meanwhile I contacted Apple service executives they told me that if the issue with the product is of major concern, then product will be replaced, if only display is not changed and rest of the parts are not changed means it's having a big issue right! We don't know that the replacement parts are also someone's iPhone ** repaired parts. I want complete new sealed product as it's under warranty and product is with manufacturing defects.
I want a new sealed iPhone **, as i got the product with manufacturing defects.
Please help me on this.