wrongly billed

I received my account statement for March 2015. I was billed R930 odd rand when my contract is R569 per month. I called in to the call centre immediately, and spoke to a lady who informed me it's because I used my internet. Smart data something. This is appalling, I get 3 gigs of data every month. 1.5 gig daytime and the rest night time data.<br> <br> I then had a look at my previous month statements, and in the February statement that was sent to me, had the end of March's account details in it (this billing period ) so now I ask, how on earth do you guys bill. .how did you get my figures for march 2015 already in beggining of February. I demand you revert this error, as I am definitely not paying for something that has been incorrectly billed.<br> <br>