Vodacom the worst network provider!

I purchased airtime for R29, I bought R5 voice minutes and R5 whatsapp ticket! To my surprise R19 was deducted from my airtime and I was left with a R0.00 balance. When I phoned the customer care line, They couldn't provide me with a concrete answer as to what happened to my airtime, They just said it was used up by connecting to the internet. My applications were closed, data restricted on all apps. Why can't Vodacom use the same system as Telkom Mobile - Heita where the data gets paused if it is depleted instead of using up our airtime. I say this is ****************! I am porting to Heita!Finish and Klaar!