Poor Technology monitoring

I have a problem with Vodacom and am asking myself where is IT staff or people who are responsible with the latest Technology. Or Vodacom should be having latest Technology from long time ago. Or maybe is a plan for people to keep buying time for more profit am not sure. Am a contract user my problems is.

1. When I receive my monthly airtime I buy Data using the same airtime right according to the way I think those Data will push me until the end of the Month, but it happens they run out quickly so my question is WHY WHEN MY DATA RUN OUT MY DEVICE CONTINUE TO TAKE MY AIRTIME. This not allowed in this Technology we live in if DATA finish it must Stop and I receive SMS telling me my DATA runs out and internet must be disabled. And me if I enable it manually it must then continue using airtime.

i believe Other service provider doing that, or Hire people that think about customers.