Airtel - Not processing migration of postpaid to prepaid

I have an Airtel postpaid SIM which I wanted to end the service of. I visited the nearest Airtel store where they suggested to first convert the postpaid to prepaid and then if you don't want the SIM, it will just get disconneted if you don't recharge. So they directed me to raise a request in Airtel app for it. So as per their directions, I raised a request for migration of my postpaid SIM to prepaid on ** June.

On that day, I received a call from their customer care. They said that if I don't want the SIM, they can just disconnect my SIM instead. All I have to do is give them an OTP. However, the OTP I received was for cancellation of my change of SIM request. SO they scammed me and cancelled my Postpaid to prepaid request on their own.
Since, then I have been continuously contacting their Customer care, their appellate authority and even their nodal officer, but my issue simple stands ignored.
Now my bill due date has already crossed and they will claim for bill payment for another extra month for the delay they themselves have caused by fraud.
Airtel is simply scamming people by lies and exploiting them for money.