Incorrect Billing

I am an Idea user since the past 5 years and more, I had initially a corporate plan with 2G connection , and if I exceed the limit of internet usage my speed would drop and internet would not work(this was a basic understanding) Till April 2015 everything was going fine, suddenly in the month of May I receive a bill amount of 7331/-. I was shocked, there was no intimation from Idea for any excessive usage, no prior notice. Since then I have been following up with Idea through calls, emails and social media. They took a month to understand the entire matter. According to Idea there is an activation of a 1GB connection for internet which ideally I as a user haven’t given any authorization, (and if there is any authorization kindly provide evidence). I have put in this dispute and they have not reverted with any response. But their reps keep calling for making the payment and when I ask them to check my complaint status they just disconnect the call on my face. They have disconnected all my services, outgoing, incoming, data services. request you to kindly take this matter up on urgent basis.