Airtel — balance deduction even for doing a miss call

I cannot do a miss call to any of the isd numbers (Uae and singapore). Whenever i try to call, my balance got deducted as per their standard call rates. I have informed this in their customer care (Airtel) and have the voice clip relating to this conversation. As per their reply i cannot do miss call to any of the international numbers and this is their rule for morethan 3 years. But i am not aware of their "rule" till this date as i had made some missed calls to international numbers last month also. And that time my balance was not deducted. Also i have checked their "rule" by calling from another airtel number. That time also the balance remains unchanged. So why are they imposing their above said "rules" to some selected costumers.