Airtel — call barring service

I am unable to use the call barring feature. I was using this service since 2004 It was working fine before but since last week I am facing problem while using this service. I tried contacting Airtel customer care many times but as per them its a handset feature and suggested me to contact Nokia for the same. I explained them by sharing the manual of the Nokia model that it must be activated by the network service provider but they don't agree. I remember very well that this service was activated on my nujmber from AirTel in 2004. It is not a handset feature. It can be used from your handset only if it is activated from your network service provider (Idea, AirTel, Vodafone etc.) Not any customer care executive including senior supervisor too, knowing properly regarding this service. Everybody is saying same that this is a handset feature. Even theirs nodal officer also saying same. It is really the height of ignorance by Airtel.
Please get the Call barring service re-activate on my number.