OUT OF BUNDLE CHARGES NOT AGRRED TO

This past weekend the Cell C app was down and I was unable to check my usage at all, I also did not receive any notifications that my data usage was at out of bundle rates. The Cell C is is suddenly working today and I have a data usage bill (over and above my monthly subscription amount) of R650! To make matters worse I SPECIFICALLY OPTED FOR THE OPTION THAT MY DATA USAGE BE AUTOMATICALLY CUT OFF ONCE IT REACHES OUT OF DATA BUNDLE RATES. Please advise why this is not done Cell C???? How is it even possible????