Apple India — call delay

I have purchased new iphone x and getting call delay problem from first day. I am contacting apple customercare from first day of purchase. But no solution get from apple. If it is not resolved with in a week than i will put a case to consumer court for return my whole money with my harashment coat.in starting call delay starts from 6-8 seconds and after some hours it becomes 20 seconds. From this problem i am missing my important calls and time loss.
Vikas singla
[protected]