Un explained high bill

Last week as I check my outstanding balance as per every month it states that my outstanding balance is R1 100, I called the call center on Thursday I was promised that someone from the finance office will call me till date not even just an SMS for an acknowledgment. My concern is how does it reach to this amount when I pay strictly their outstanding amounts every month why was the connection not cut just by missing 1 installment. One thing is for sure I will not afford to such an high amount I will rather not connect any more because I work on a monthly budget. My account number is ********** 0