Airtel - Unusual balance deduction

I am an owner of Airtel number. I recharged my number with *** Rs on * April **** and got a balance of *** along with * GB data. As I got * GB data I started using my data and when it reached ** MB (as per my Airtel app) I stopped using my internet, but I got very disappointed when *** Rs deducted from my main account balance.
One thing to note down that even after deduction my data balance on my Airtel app is still ** MB. I complained to Airtel customer service and got a dissatisfying solution. They simply told that I was charged for data usage. I told them again and again that as per my Airtel app my data balance is still ** MB but they told that information provided by me is not correct. After that, I mailed to their appellate authority. They called me back regarding my issue and told me to try after installing my Airtel app and again install I tried the same and still my data balance as per my Airtel app was ** MB. Again they called me later and told me that it's some technical issue from their side that my Airtel app shows ** MB data left. I asked them for a refund but they told that refund policy is not available even after accepting their fault.
I want to highlight here is even while writing this complain it became ** hrs after my deduction and still my balance is ** MB as per my Airtel app data. Also, I didn't get any warning message of ***% consumption of my mobile data. I want to ask them that I used my Internet as per the data available on my Airtel app which is ** MB as per my Airtel app then how can they charge me unless my data got * MB. If it's a technical fault from their side then why they can't update even after ** hrs after my last internet usage. I as a customer believe what they show. How I can know that the data balance showing is wrong.

So this is a clear fault from their side. I am not providing my number on which I face this issue due to security reason. But can provide of Voxya if asks me in future and also I am attaching a screenshot of my Airtel app showing data balance of ** MB as on ** April **** i.e ** hrs after my deduction.