One Plus - Phone dead in 1 and half month and not replacing amazon

I have purchased my mobile(one plus *) on july ** on amazon and faced couple of times problem like it automatically switches off and on. Due to some issues i didn't contact one plus store and on *st September my phone was completely dead while I was using it. I visited one plus service center banjara hills hyderabad they told me to replace motherboard which is the major part of the mobile phone. I asked them to replace me with new mobile because its a major issue. They told me to contact amazon for the replacement but they can help me with the required documents. Then i contacted the amazon customer executive and informed the situation then customer executive sent me an email regarding replacement and asked me get some couple of documents from one plus service center and i got that documents and emailed them. Amazon customer service guys asked me to wait for **-**hrs for investigation and solution. I have contacted multiple customer executives to know what is the status of my replacement then one executive replies we don't even have your case filed and another executive says yes sir we can replace but wait till **hrs for solution one says we don't even have the ticket of this and atlast after **hrs now they says we apologize for whatever our representatives spoke to you about replacement we can't do that as replacement window has been expired in **days and we can't help you anything.
Very disgusting experience with customer service of amazon and very disappointed with the things happened in *days and now I'm very pissed off with the process and *days without a mobile phone and they don't want to care for customer problems they only required their own policies
Please help me out with this issue.