Vodacom politely billing customers unaware

I called the Vodacom CS to put a cap on my husband's bill as he has made the mistake to choose opt 2 when buying data and then gets billed for it. So he gets surprised when his bill is higher than usual. The CS agent said it wasn't possible as he is on a top up contract. She also confirmed over the phone that numerous other customers have called in for the same reason all the while Vodacom is laughing straight to the bank. Naturally I assume this problem won't be sorted out as you obviously just nicely debit people's accounts without them being aware that their bill is now more. Some people have budgets so imagine when for 2 consecutive months an extra R200 is debited from your account. This is ludicrous!