Airtel — Bill - Overcharged

My phone is [protected]. I am a post paid user of Airtel for close to 1 year and using Airtel for 3 yrs now in total.I was using Rs 125 - 2G data plan of 1 Gb limit. I had got a bill of Rs 4005 for the billing cycle[protected] to[protected]Bill #[protected], which is very strange. Upon calling the customer care, it was told to me that i had used 2.5 Gb of data because of which i got such a huge bill, which was wrong. My phone shows that i had used close to 1.25 Gb of data for that cycle. I use Wi-Fi most when i am at home. I tried calling the customercare so many times they never gave a chance to talk to a supervisor, they made false promises that i will get a callback. I am very upset at the moment. I was a loyal user to Airtel for the last few years, this is the first time i am facing this kind of issue. I had used extra ~250 Mb that does't mean they should charge me for additional1.5 Gb. Please get the bill rectified.I spoke to so many representatives but they were of no help. I have a Case #[protected] for reference. If you can look at my history of bills, i never got such a huge bill. Something has gone wrong at the billing section this time. I had sent so many emails at [protected]@in.airtel.com but no proper response.