Charged out of bundle rates for data not used.

On Friday the 27th of March 2015 is was charged almost R1000 for data use while maintaining a positive data bundle balance. I have a very clear history with Vodacom of never really exceeding 250mb data usage a month and maintaining a positive data balance to avoid charges . I have access to free WiFi day (at work) and night (at home) and I also had an active data bundle at the time with data available. I bought a further 1 gig at seven thirty Friday evening when I noticed my WiFi at home was not working and I decided to use my phone as a portable WiFi hot spot. My data bundle was running low (my Vodacom App show 90mb available at this time) so I topped it up. My data never went to zero to justify the out of bundle charge and the streaming only used about 300mb. I don't want anything for free, I just want my bill to be set back to where it was before the charge, R508 or there around + R150 for the 1gig data bundle. Please help.