No service for network

Hello iPhone support community. I am facing issues in basic essential function of my iPhone 13 - the network connection. I have recently purchased this device and have noticed the issues after update to ios 15.0.2

i have tried network reset as well, but it didn’t help. Turning on and off airplane mode works but it is only possible if I am continually looking at my phone to know that network has gone.

need a solution, as it has rendered the phone very unreliable and useless