Airtel — problem in calling

My name is babita chhabra. My airtel sim does not support the calling feature as soon as i started using 458 plan. As i try to call someone call ended appears and even when someone try to calls me my no. Gets a busy tone always. I have already talked about the same issue to customer executives twice but my problem still persists. I am able to use net and messages properly. There is no problem with them. Only problem is in calling.