Airtel — refund of ISD Deposit

I had paid airtel an amount of Rs 6500 for the activation of ISD roaming on 5th May 2008 for the number [protected] as i was supposed to go to Australia. When i went there i found that the service had not been activated so when i came back i asked for a refund in the August 2008. i was told i will get that back by 28th August 2008 which i havent been refunded till date. when i refused to pay my bills of my connection my services were disconnected.also i have been after the customer care people but they are of no help to me.
i feel that airtel is a big cheat company and is haressing its customers well. i need my money back. findly tell me a way to get my money back