Airtel — airtel sending irritative messages and system calls

"dear customer, we have observed no usage for your airtel mobile from the past 30 days. To enjoy continued services, please make an outgoing call /sms or use internet from your mobile."
This is the message i am getting daily even if i use my phone to call occationally in a month while roaming. Also i am getting system calls alerting me to make a call from my prepaid number. That costs me if i answer to those calls, since i work in another country.
Why do airtel pushing me to loose my money. Anyway they are deducting rs.99 monthly towards for roaming service.

Is looting becomes legal?