[Resolved]  Airtel — To activate& deactivate SMS10 service

I want to activate SMS10 service i.e offered me from Airtel.
But If i send Activation request as "SMS10" to 51619
i got reply as " Inalid Requestor Mobile No."
I contact Lots many time to customer care but no one tell me what is problem..
I want that ..
Airtel Find out solution to this..
& i can able to activate & deactivate this service whenever i wants. There is no need to contact customer care again & again..

I am always with Airtel... But Plz I want this service....