Airtel DTH Connection — Illegally Disconnected DTH service

I purchased a SAMSUNG 40" TV on 25.12.2008.Airtel DTH was offered as bundle offerfor five months, and connection was given on 02.01.2009.I was given south jumbo pack.after two and half month they disconnected the service.On enquiry over the phone and e-mail I was told that I used their service and as my account showed negative balance of Rs.504.35, my connection could be restored only after paying the balance.
My question is how I could have use their service apartfrom useing their free south jumbo pack? Even if I have used any of their payment oriented service as per their claim what are they? when and how?.
Despite my repeated e-mails they did not give me any details about my account except repeatedly stating that I have to pay Rs.504.35, and though my connection is valid for five months they have stopped the service from March.
Under the circumstances I kindly request you to do the needfull.
Thanking you
Yours faithfully
N.S.Kalyanasundaram M.A.B.L.,