WRONG BILL

We have been billed monthly however we are on pre-paid, when we bought that house - 3 yrs ago we were on pre-paid. On 04/09/2015 I called Eskom call centre regarding a bill that we get monthly, I was promised to be called back within two (2) working days till to-date they have not called me. HOW CAN YOU BILL A PERSON WHO DOES NOT EVEN HAVE A METER THAT ALLOWS THEM TO BE BILLED MONTHLY? , the only meter we have is for PRE-PAID. WE need answers... Eskom Ref#: 153 259 704 ----- Acc#:***