bonus airtime but deducting airtime

On the 24th ive received an sms from vodacom which was sent by 01:20 where i was told that i have receive a bonus airtime of R150 and is going to expire on the 24th by 23:59, i made few calls to vodacom numbers as per sms and to my suprise the calls were deducting my airtime. i contacted vodacom and was told that it was a technical error and there is no way they can refund me my airtime. i hate stupid system which cost me at last