Apple India — iphone 7 internet is not working when device is locked

Address: Ranga Reddy, Andhra Pradesh, 500084

I have purchased iphone 7 in nov 2016. But after few month latter the phone internet is not working when phone is locked.
I am getting all the notification very late.
I have raised the issue to apptronix hyderabad and apple telephonic support care but they are directly saying we can't resolve this issue.
I have shared the videos also and shown the issue, but still i am not getting any help from service center.