Airtel — outgoing calls barred without warning

Address: Bangalore, Karnataka, 560067

Outgoing calls on my number (used for 10+ years) have been barred without any warning. There are no dues. Contacted 121 and was told that there is a "documentation issue" and I should contact Airtel office and there is no other way they can help me now. How unprofessional is this act especially since the phone is critical to my business.