Airtel - Wrong billing for data use

My number was wrongly billed for over Rs *.* lakhs for data usage during on the pretext of international roaming. There were no calls received or made. I used hotel wifi and another local SIM card for data use. When I got in touch with customer care after I received messages regarding this amount, they asked me to wait for my bill to be generated so that the issue can be addressed.
The bill was generated after a month's delay, and I registered a complaint and another one subsequently because the issue was not sorted. This bill amount is illogical in every way. One should not be charged like this because one switched on one's phone.
I have been a consumer of this mobile service for almost two decades and my bill is usually around Rs **** per month and has never gone beyond Rs **** even during international travels before. My phone bill overdue credit is at around Rs *****. Why has the company gone beyond the credit limit in the first place? I do not see the logic in charging for something that has not been used. How does one have a functioning number from February till date if the bill amount exceeds its limits, if at all?
Even after filing complaints and being in touch with customer care I now have my data cut. I have been receiving calls to say my incoming calls will be barred. I have collection agents being sent to my house to collect this sum.
These few months of following about this absurd amount against my data usage during a time when my phone network was not even working have caused me too much mental tension and distress.