Airtel — Refund for 300 top up (credited only 264)

Address:

Chennai, Tamil Nadu

I made a top up online recharge for 300 Rs talktime... but i got credited only 264 rs to my mobile. where as in the company site its listed as..
Denomination(Range) TalkTime Range Value (Rs) Processing Fee (Rs) Service tax (Rs) Validitiy
300 300 0 - Unlimited top up recharge .
Web site link: http://www.airtel.in/mobile/prepaid/recharge-online?CIRCLE=6&CIRCLENAME=Chennai&tab=1#tabs-1

I want the remaining 36 also credited to my account. I have saved the company website data, which shows for 300 Rs top up 300 talk time is provided. But now I have lost 36 Rs simply... and when i called the customer care .. they are telling me that its a " benefit ". Totally feeling cheated.