Data Account being soft locked at wrong amount.

I have a 2 GB data bundle for my IPad and ****le. I also had a R50 soft lock limit put on my data account, therefore, if I use all of the 2 GB data, my line will be soft locked after R50 of usage. After downloading 2 GB on my account, Or as I thought, Vodacom soft locked my account, but without my knowledge it soft locked only after using 3 GB of data. My bill ran up to thousands of Rands. This happened on 4 occasions during 1 year. I did not notice it before, since my debit order is for one amount. This amount includes my data contract and cell phone account. I am very upset about this as Vodacoms excuse is that the line will not soft lock while downloading, it will only lock once done with the downloading session..unless the download is interrupted. This in fact is not true, as I've had this lock on my account for 2 years, and it did if fact cut off during downloads. I would like to say that this, to me,is unacceptable.. Till now if I phone Customer Care, they tell me that the R50 soft lock is still active on my account. What is the purpose of having a soft lock on your account if you can download as much data as you want in one session, according to Vodacom! Pointless!!!