Xiaomi India — mi a1 network problem

Team, i have mi5 which i'm using from around two years without any issues. But my recent purchase of mi a1 for my wife is having some serious trouble with network reception.in room where my mi5 pickup good coverage, mi a1 cannot even connect to network. But outdoor coverage is ok. But i cannot always be outdoors to attend calls! I have been to service centre but they are of no use. I have tried all possible options to fix the issue but nothing helps. It seems like some hardware issue rather than os. I'm on nov patch level which is latest. Please fix the issue or refund the money back!