Xiaomi India — Irresponsible service centre

Address:

Kolkata, West Bengal, 700028

I gave my Mi 4i mobile on 03/08/2016 for just a change of battery. Today is 14/10/2016 but didn't get any reply from the service centre at Saltlake, Kolkata. It's unbelievable that a company that makes such big advertisements can't replace a battery at the store itself or even in the service centre! Moreover the service provider employees are such careless that they don't even pick up the phone call.
I regret to buy such a disgusting company product. Is there any solution you can give me or I have to take my own measures?
Goutam Adhikari