The amount is unfortunately due - error not on Vodacom's side
but it does appear that they have at least started to recognize the value of not being douches on this issue and it couldn't hurt to write to them acknowledging responsibility and setting out that you have corrected your settings etc ...
From a general being good point of view they should really discount it to something like what double the cost of the requisite bundled data would have cost (double because of network planning and what not), also the OOB shark persisting without adequate lock out tools on the data side is still a serious bloody problem and there ARE solutions
Unfortunately there doesn't seem to be something set in stone, to encourage confidence and peace of mind when it comes to situations like these.
If the consumer had a time period 2 months - 3 months in which they could reduce the OOB rate to normal prepaid tarriffs + a set 50% fee based on what they pay monthly with absolute certainty it would be la tiny bit more acceptable.
So if you OOB by a gig and your monthly contract is R499 you pay R400 (R250 + 150)
If you OOB two gig and your monthly contract is R499 you pay R450
Would still a lot, but it would be a guaranteed resolution and less insane.
Atm the punishment doesn't fit the crime, just the pockets of the greedy.