Annoyed about data usuage

I have a talk 240 contract which i get 240 min every month and a gig of data every month..., it is the 4th of the month , my data is almost finished so i log onto vodacom and to my shock my bill is sitting at R1150.26, they are absolutely crazy my bill is max 800 a month and thats with buying a extra bundle every month... i go onto th eproposed invoice and found a R400 data usuage bill so they have charged me for data that i have used, i have a data bundle for a reason , they have charged me double they have taken it off my data bundle amount and charged it for my end of the month data usage.PLEASE SORT THIS OUT , make me wonder how many other times vodacom has *****ed me and other customers...