Missing Data Vodacom

I have a data contract from vodacom and after purchasing additional 20 gigs at 6h30 I switched on the modem and went to my vodacom app and realized at 6h35 that the gigs were 9.17. I was shocked what happened to the other 10 plus gigs it just magically disappeared. I have a child in matric that needs the data and feel so **********. I called the call center and the lady that answered just rep**** that the data was used(yes the data was used it was the 9.17 gigs that was given). I am very disappointed that vodacom can use this lockdown to get us to buy data knowing that our kids need it to study and the connect for u that vodacom says they give for education for free does not work in our area that I live in. I just want to know where is the 10 plus gigs that I paid for.