Vodacom charges are outrageous!!!!

After upgrading my contract from an iPhone 5 to iPhone 6 Plus I was hit with this outrageous bill. As i am mostly connected to WiFi i barley used to use up my 500Mb data package. Using the same settings as before (Automatic updates only use WiFi etc...) i'm all of u sudden using 100 to 200Mb a night???? Hard to believe when i'm simultaneously connected to my WiFi at home and office where i spend 95% of my time. I then phone customer care and am told it's due to the new phone being more advanced and that WiFi is only a hotspot. If the hotspot is lost the phone will automatically continue using mobile data. I wasn't born yesterday VODACOM!!! SORT OUT YOUR S#@T!!!