Airtel — incorrect billing for international roaming

I had deactivated international roaming on my mobile number in nov 2017.
I have acknowledgement from airtel for receiving my request.
But no action was taken in their system on this request. It is a system failure of the company.
In my bill for jan 2018 i have received a bill of over rs 10 lakhs.
Firstly, they did not act on my request for deactivation.
Secondly, their internal warning system failed to alert on the billing limit at any stage before this amount was billed.
Thirdly, they have now disconnected my long-standing number.