I am not sure the answer already exists but here we go.
I pay for our daughter's prepay account - $30/month. She usually run out of data a couple of days before the renewal.
I don't want to leave a balance on her account because I don't want mobile data casual rates eating any balance. On the other hand I have to keep an eye on this account every few weeks to make sure I don't miss the renewal date or risk her having no service - phone calls, SMS at all.
Can I either disable casual data on the service or does Vodafone have a "reserve" on the balance so it's not used up for anything but prepay renewal?