Airtel Payment Bank Scam

Yesterday morning, I received a call from someone claiming to be from Airtel Bank. The person was telling me that they were calling for my KYC and asked me to provide the OTP, otherwise my account would be closed. I said I would go to the Airtel store within an hour to complete the KYC. Then he said it wouldn't be possible anywhere else and that no one else would call again. I refused to give the OTP. Then he told me to open my calculator, enter the first 4 digits of my mobile number, press minus, then enter the OTP I received, and then tell him the time that appears. I said I wouldn't tell him and hung up. Was this a fraud or not? Please share your opinion, everyone.