Overcharged for data

I have had a Vodacom moderm since around 2008.<br> Last month I went to a branch to cancel the subscription since my laptop was not preforming well anymore and 2ndly we struggle with the network in my area. I would go for up to 3months without using the moderm and I thought it was worthless hence the decision to cancel subscription. <br> I was then convinced to convert to prepaid since I also have a mini wifi router and use the moderm sim on the wifi and I agreed. <br> For the first time since 2008 the bill went up to R2375.76 for October just within few days after I went to the shop.<br> In the recent years my bill has always been R75. Sometimes up to just below R140.<br> I went back to the Vodacom shop to query and was told that I used too much data and that my previous info does not appear on the system since I am now on prepaid.<br> Surprisingly all these years I always had to wait for new data to be loaded when my data was depleted for that month.<br> It makes absolutely no sense to suddenly incur such an amount for data shortly after an attempt to cancel my subscription. From R75 to R2375.76?????