Reliance Netconnect Broadband Prepaid Connection — regarding bill

I have a reliance broadband netconnect connection(pre paid) purchased on 31 Aug 2009. I got it recharged with 0.5 GB top up on 03 Oct 2009 by paying Rs 500. till yesterday i.e. 27 Oct 2009, i had sufficient balance approx 0.3 GB. Last i used it was yesterday evening. When i tried to get it reconnected today morning, i was unable to do it. I went to reliance world office today evening and i was told that i have a negative balance of Rs 378. I asked how come i having a pre paid account can have so much of negative balance. Then i was told that if a consumer is using internet & the balance gets exhausted then also the connection is continued for that session till that session ends whatever be the duration and it is added to consumer's account as negative balance (the charges for usage once the balance is zero till session ends is pretty high.).. Now my complaint is that i was not intimated by the service provider that my balance has become zero during yesterday's session and i kept using it under the impression that i am still under my account limitations. The provider should have intimated me well in time about my zero account status so that i could have stopped using the services and terminated my session then and there only to avoid paying heavy charges in lieu of my usage after having nill balance. what i want from the service provider is that they should terminate my connection when balance becomes zero and do not continue to give me services against a negative balance at a higher rates..