Airtel Billing problem

My mobile no is 9987142200. I got my blackberry enterprise service plan Rs.499 activated on 6th Jan.09 & my bill got generated on 10th jan. In four days, I have been charged approx. Rs.6403 & when I enquired why my bill is so high, customer service told me that it is because I have activated blackberry service.

I complained to them that their billing has some error because in 4 days one cannot have Rs.5000 as blackberry usage bill, because even the top business executives don't run into that type of high billing in just 4 days, but CSS is adamant. Out of Rs.6403, I am assuming that my telephone bill would be say Rs.1400/- which is normally my monthly usage, but the balance Rs.5000 is abnormal.I have accessed bank, broking & some other sites on day one just as normal surfing, but never to the extent of Rs.5000. Even before blackberry service was activated, my GRPS service was also on, but never have I paid so high bill, so blackberry is no exceptional thing that suddenly I will surf so much that in 4 days I will run into Rs.5000 bill.
Even the executive at 7070 ( blackberry helpline) agreed with me ( spoke to Mr.Deepak on14/1/09 at approx 7.26pm) that there is some billing error, but customer service is not agreeing.

I will not pay Rs.5000 without any billing verification. Kindly help.