Received legal notice from Tata Docomo

I received a legal notice from Tata Docomo today. It was regarding the dispute on a bill of Rs 4456. When I took the broadband connection from them, I had checked with one of the customer care executives about the roaming charges. The representative told me that there are no additional roaming charges on my connection. When I was using it in my native, I received a message in my mobile that my bill cap has exceeded the amount of Rs. 2500. I called up the customer care again and asked them why did I get such a message when I am already having an unlimited plan of Rs 750 to which I received a rubbish response that "The message has been sent my mistake, u can ignore it". But when the bill was generated the undue amount was Rs. 4456 instead of the usual Rs 750 + taxes. I then paid the Rs 750 to keep things clear from my side, as I had opted for that plan, and refused to pay the rest since they provided me wrong information twice. Since then there has been a series of mails, arguments, abuse etc. and today I have received the Legal Notice. I had raised complaints in CoreCenter and, but didn't get any response from them regarding the same. Could you please provide me a solution for this?