Harassment by Tata Docomo executives and inflated billing

Location/place: Mumbai

Name of company/service: Tat Docomo – Post-paid

I have taken Tata docomo pre-paid to post-paid connection in Feb 2012 on the suggestion of the Customer care. After 10 days I received an SMS stating my usage is nearing credit limit (Rs 1000) and the next day I received another SMS stating to submit a payment of Rs 5727.54 and subsequently my outgoing got disconnected.
On the day I started using the post-paid connection, I requested customer care that I need a 2G GPRS data usage pack and I was confirmed the same will be commenced within 2 hours. When my bill was issued, I was charged Rs 7479.56 for data usage and a total bill of Rs. 8558.83 for less than 15 days usage. Docomo wanted me to pay the bill immediately.
Later I have spoken to a number of representatives from Customer care and strictly mentioned I want my GPRS pack included and a modified bill to be issued. Till date no action has been taken. The customer care was very inconsistent in offering me various advises on the payment, including me a way-off of Rs 2500 which is against the ethics.
There was no co-ordination between the representatives of Customer care (Tata docomo) as what was going on. And one fine day, an executive came to my work place and I had to explain the same thing which I explained various Customer care representatives on phone. Later I started getting harassment calls from representatives of Customer care (Tata docomo) about the billing. They had no idea that I have already spoken to another representative earlier on the same lines. Later the calls continued at my work place. Even my neighboring colleagues are getting harassed. I am completely offended by their behavioral setup of representatives of Customer care (Tata docomo). I kindly request you to advise me fairly.