Apple - Faulty phone

I have purchase a new iphone on * January ****. Just after my purchase its rear camera stops responding. I have showed in service center they told me phone is to be replaced. Now *-* days they are saying that they have replaced screen and camera in my phone. But when I have paid full amount to the company why they are not replacing my phone why they are giving me a repaired handset that too a major repair. Company response is also too poor they are not at all listening to my complain and not bother to escalate my complain further. They told me that once decision taken my technician is final. How a technician decide my fate. Please help me to get my phone which I have purchased from my hard earned money.