Airtel - Postpaid Number In Chennai — Number Disconnected without any reason

Hi,
I am using Airtel postpaid number for more than One and half year. My number is suddenly disconnected and it shows "Sim Registeration failed". I have called from friend's number so many time to 121 but I didnt get any response from Aitel. I had also written mails to Customer support but never got any satisfactory reply from them . Even nodal office (Asif ) hasnt replied with vaild reason why my number is not working.

It took them 2 weeks to find out that my number is disconnected because of some internal changes in system and I need to apply for new number without any fault of mine.

Even after all this, these support people are asking me to deposit bill for the duration that my number was not working.

Can anybody give me a vaild explanation ????