Money disappearing

I normally get notifications when the money is been withdrawn or deposited into my account, two weeks ago +-R100 disappeared from my account without any notification, today i got R350 Deposited into my account, i got notification and bought R30 Airtime also got notification, i went to atm to withdraw the remaining amount and there was only R30 left, i didn't get any notification. I wonder how does that happen as i keep on missing money. I called their customer help line they asked me few questions and told me I've failed should call back after 24hours. I called again so that they can stop my card but before i can finish talking to the consultant my airtime was finished. They didn't even bother to call me back as I've already given them my name, surname,id number and cell phone number.