SIM800C Network Registration Denial

Hello All

I am having an issue with the SIM800C module on a custom-made PCB. After I power on the module, the module starts to search for the operator (AT+CREG: 0,2) after 1 or 2 minutes module stops searching for a network and goes to state Registration denied (AT+CREG: 0,3). I tried using Airtel/VI Simcard but the outcome was the same. I can check SIM is OK via the AT+CCID command (properly installed).

Any help?

Thanks