Airtel — Billed wrongly after committed for 2 months free subscription

I have requested to discontinue with this company on 17-Jul-13, as I was not satisfied with Support from Airtel (was facing Network issue at Dankuni Location, but receive no response from Airtel) After that I got a call from Tech Engg from Airtel (Ref#[protected] & he accepted my request & offered me two options 1. Take 4LTE in place of 3G dongle with concessional rate. 2. Go for 2G unlimited connectivity for 2 months free subscription. I accepted the 2nd option, hence he has converted my Connectivity speed to 2G. But he has not sent any confirmation on this (neither in SMS or Mail). Hence I sent mails thrice to get confirmation on this to 121, but never got any response. Hence I continued to use that 2G connectivity thought of that has been accepted. Then I got a bill for Rs. 1685.41, which is huge compare to my usual billing amount (which is around Rs. 500-600). I sent mail to 121 asking for help. Then there was many discussion with Tech People/Billing People. And every time there was a new person whom I need to explain the entire scenario every time (over phone &/or mail as well), as they were not aware of previous history. Although I explained every concern to those person but no one has came back (although promised to get back to me later) with proper conclusion. I forwarded the mails to Airtel Nadal Officer, after that forwarded to Appellate Authority also. Yesterday I had talk & today I saw a email from Nadal Officer, stating that provide the information who given this info to you. As usual I forgot this info. But they never accepting that they have not responded to my mails, which I sent to get a confirmation on this. Seek your help on this. Thanks!!! Airtel Presence & Nadal Officers are telling that the Bill levied is proper as per the Bill Plan. But as per the commitment from Airtel Tech Executive, that Bill Plan was suppose to be changed. But I have not got any intimation that it was not changed, even I have sent a mail to get a confirmation abt the free Bill Plan to 121. Even that was not responded. I would like to know what else Airtel expect from me. While I already decided to Discontinue with Airtel. I only used Airtel last month as per the free commitment from that Tech Guy. Attaching below the correspondence I made for terminate Airtel Connectivity & the Mail which I sent to get a confirmation from 121 in this free bill plan. If that was responded then certainly I will stop Airtel that day itself. Hence request you to revise the current Bill. Please help to get rid of this issue. I already have waste lot of time discussing on this...