DATA GOES MISSING EVERYTIME

I am completly disappointed at the way that vodacom is reaping us off, this is not the 1st timne something like this happened. This morning i bought airtime and converted it to Data with seconds i was sent an sms to say that i no longer have data im left with 3mb and when i called they told me that i have auto update which updated on it's own but how does it update if my data is off. I had the same problem the other day. Just because vodacom is a big compmany feel that they can just reap people off like that. I have been using vodacom for a long time now and im forever having problems and i guess the reason im still using it is because i hardly struggle to get network when im travelling if it wasn't for that i would have switched to a different network long ago. I can even begin to explain how disgusted i am.