Tata DOCOMO - EXHORBITANT BILLING ON 9896394108 BY TATA DOCOMO IN IST MONTH ITSELF

I got new Tata docomo prepaid connection on portability on 24.10.2011 and even for a service of net not utilised by me, they billed me of 1000/-in one month. For usage of a few minutes of net i.e.facebook very light sites, they charged 150/-approx daily. I felt cheated from company as no grievance is being resolved by call centre and no satisfactory reply to mails. Even they are not allowing me to surrender the phone or to shift to pre paid. Please help to resolve. My entire usage record may be verified as company has billed me for service not used or little usage. I have been using net on airtel and billing never exceeded normal pack.