Services barred

Location/place: Mumbai

Name of company/service: Airtel

All services on my phone were barred on Jan 18, 2013 without any intimation and when there’s no bill pending. I could not even call customer services for assistance. Had to borrow phone from co-workers to speak to customer services.
The information I got was that I have reached my credit limit of 3000rs and would need to pay interim amount of 8000rs to get my services back immediately. No one was able to explain me why I need to pay 8000rs.
Bill generates on Jan 21, 2013. I was told either pay 8000rs or wait till Jan 21, 2013.
Services stand barred. how am I supposed to follow up on customer services as the promised call backs were never done.
Expected Bill on my a/c would be 600rs as per the airtel customer service executive. why should I pay 8000rs or 3000rs for the reasons unexplained to me.