SIM800L not registered to network

I am using SIM800L connecting to USB to TTL trying to connect to network Simard which I am using is Airtel when I am using this command AT+CREG getting response of +CREG :0,0
Below I am attaching block diagram which I am using right now
as wll as attaching commands which i am sending and its response
I am trying this from long back please help. Thank you


incoherent