soft lock limit

Could someone in Vodacom tell me why we have a soft lock limit. My daughter borrowed my phone at my in laws who have wifi and went outside for a bit and when she came back I saw my data was on. I turned it off and then got told I was soft locked. But now how the hell did she manage to spend almost R600 in data. And my 100mb that were on my phone. I have a soft lock limit of R100 on my contract for a reason. Why didn't it work. I'm unemployed and I must now pay a bill of over A R1000 cause your guys software is not working if it doesn't work properly then why offer it. I downloaded the Vodacom app so I know that I had 100mb left. Please don't phone and tell me that the software doesn't work that fast cause I have been on the phone when it has cut me off and said I've reached my limit. I can not afford to pay R1000. Please sort this out.