Voluntary call limit set incorrectly

I set a voluntary call limit for R800.00 on my account on 22.06.2015. I've received an sms yesterday saying I've exceeded 70% of my voluntary call limit. When I check the balance of my account, it is standing at R1502.29!!! I set my call limit on R800.00 not R2100!!! So clearly Vodacom is giving the wrong information to their clients. They have to inform you that if you set a call limit, they will still continue billing you up to 262% of your account before cutting it. So why set a voluntary call limit? And please don't tell me your system aren't working, because I am receive the sms to inform me. The limit is wrong on YOUR side.