Airtel — Unbilled amount without any reason

I have Airtel no. Iam not using any isd calls and another service which is payable but my unbilled amount increasing day by day when ar starting contact to customer care they said you are not using any isd and another addon service suddenly yesterday they said you are using isd calls i have close isd service on my no. But I was not using any isd service and not done any isd calls i don't know how they are saying that iam using isd call they are not helping me only after generating bill we will track issue but iam in mental stress if someone using my no. By hacking and do some illegal activities what will I do do something about this if problem not solve iwill file case in consumer court