I had the same problem from 1-12-2021 with Airtel mobile SIM as it was working for the past 8 years.
It is vital to have the Airtel SIM to receive bank OTP and many more services such as Aadhaar etc.
I contacted Ooredoo asking why Ooredoo/airtel mobile signal suddenly disappeared, but the support team had no answer.
I started to explore and found the answer as follows:
Go to Mobile data setting of the Airtel SIM, select the Carrier (choose network provider) in manual (not auto) and select as Ooredoo 3G or Ooredoo (prohibited) in some mobiles.
During the process disable Data roaming, 4G and Volte and keep WiFI Calling enabled.
The Airtel SIM mobile signal will start to work again.
I had the same problem from 1-12-2021 with Airtel mobile SIM as it was working for the past 8 years.
It is vital to have the Airtel SIM to receive bank OTP and many more services such as Aadhaar etc.
I contacted Ooredoo asking why Ooredoo/airtel mobile signal suddenly disappeared, but the support team had no answer.
I started to explore and found the answer as follows:
Go to Mobile data setting of the Airtel SIM, select the Carrier (choose network provider) in manual (not auto) and select as Ooredoo 3G or Ooredoo (prohibited) in some mobiles.
During the process disable Data roaming, 4G and Volte and keep WiFI Calling enabled.
The Airtel SIM mobile signal will start to work again.