Airtel has charged me Rs12141 for the data usage that I have not used

Airtel send me bill of Rs12141 for 2g internet usage for the data that I have never used according to the “DATA USE” information that I got from there system

I had a airtel postpaid connection(no:9975982108) under CUG plan, in which I have 2G data pack subscribed @98 rs and a rental of 149. I get 2GB free data in that. For a bill period of 05-July-2015 to 04-Aug-2015 I have incurred undesirable data charges. They send me the bill of Rs12141. My Credit limit is Rs3600. They have not send me any alert while my data usage was crossing 80% or 100%. Earlier I have all my bills in range of 100 to 400. I have only used data by frequently checking the data balance to avoid the excess data charges for that I”m having all the proofs. On 25July system gave me information that only
1)303.87MB is used against 2048 MB till 19:06hrs,25july15.
2) 547.11 MB is used till 22:15hrs,25july15.
3) 1036.18 MB till 07:38hrs,26 july 2015, and
4) 1333.08MB till 12:56, 26th july. After this I deactivated the pack.

Still after deactivating the data service on 26th july I got a message from airtel, pasting the exact message “Remaining 714.92MB of old 2G data pack can be used free of cost at current speed within this bill cycle” till 30th july I got this message. Still after this message they charged me Rs12141.
I have showed the proof of the same at main office of airtel @Nagpur and registered a compliant.Reference number was 63891449, but 7 days past that request is in open state.They are saying that you will get a callback in 4 hours but not a single call came. I”ve mailed several times to [email][email protected][/email]. Also I”ve mailed appellate officer, but everytime he was giving me the the same explanation but not answering my only question that whether the remaining data information that I got from your system by sending message to 121 with “DATA USE” is correct or not. Because if they said it is correct then no charges would be applicable on me as still 714MB is remaining and can be used free of cost according to there message and if the information is wrong they this is the huge fault of there system so they need to revert the charges. I”m really mentally fustrated by this harrasment of airtel. Please help me.