Vodacom Billing Issues

I had purchased a 500mb data bundle & had a R500-00 soft lock limit on my phone. Then around the 6th of the month I received an sms telling me that I have outstanding data usage of +-R2500-00. This has created extreme financial burden on myself as the account is currently sitting at R4000-00!! <br> <br> By browsing through the comments & complaints, I see that you have done this to many customers this month! Please explain how & why this happened