Airtel
Inactivated my pre paid numbe

I had a pre paid number from 2008 April. I had shifted to chennai from July for a year but since this number was widely distributed i kept it active in a dual sim phone as a second number. out of blue my phone number was inactivated in December and now it has been given to another person. please tell me can i lodge a complain against Airtel and also how do i get my number back