Airtel — unable to call toll free number starting with 000-800 through airtel

Address:

Hazaribagh, Jharkhand, 825301

Hi, I have a Airtel postpaid sim. I was trying to dial 000 800 xxx xxxx that allows connecting to my company conference call. But I am not able to mak ethat call, its saying -" dialled number does not exist ". Contrastingly, my collegue too has a Airtel mobile. He has no problem connecting to the call.
Question: Is there any specific service for this? Please let me know how to resolve this issue.