Sony India — Product-xperia, e2115 i am complaining about the poor service by the authorised service centre

Website:

www.sonyindia.com

I ahd purchased an XperiaE2115 on 16.08.2015 and immediately after the phone sometimes fails to start after being shut down.
I visited repairing center & submitted the phone on 6.11.2015, they returned it on 30.11.2015 telling that it was a software problem and they actually not handed over any paper noting my complain.the same problem persist and due to my busy schedule i asked the shipowner to send the phone to repairing center which he does on 5.1.2016 but they only reset the button and did not solve the problem and send it back after a few days.the same problem came back and this time i visited the service center and deposited the phone on 22.3.2016 which they returned on 1.4.2016 telling that they had changed some parts but the problem remains.It laeds to harrasment, mental agony and uncertainity.I demand total replacement of the phone.Kindly help