Hi,
I faced the same issue yesterday. This was the second time, I am facing it.
Tried rebooting multiple times without any luck.
Changed to Aeroplane Mode, No luck
Removed SIM tray and reinserted, No luck
Later removed both the SIM cards and insert a different one. Then it detected it. Now removed that SIM and inserted the original ones. It worked.
This solution worked for me in the last two times when I face this issue