Xiaomi — Didn't receive the phone back from the service center

Address:	Mathura, Uttar Pradesh, 281001
Website:	www.mi.com/in

I have given my mi4i to the xiaomi service center on 28/05/2016 but haven't got it back yet and all i'm getting is useless excuses that the parts are not available, go and talk to the customer care and we can't do anything about it. i even talked to the customer care and they said that they will look into the matter and it has been more than 15 days since i talked to them but there is no progress in my complaint. i asked the service center to return my phone but they have damaged it even more and the phone is now not even switching on. what can i do now, i'm facing lot of trouble due to this.
Please help!!