Apple India — iphone services to fix the issues under warranty.

Address: 600063

My iphone se is having problems in connecting to network from september 2017 and was purchased on 25august 2017.
I have been complaining the customer support since 6 october 2017, asked me to give phone for service i gave it for service as instructed but no resolution given.
They say iphone is working fine and problem is with airtel, vodafone idea networks for not connecting to iphone network, where only jio sim card is working.