The worst data package ever!

This service is the absolute worst in terms of treatment of customer. Months ago I got debited R400 some odd for an R89 data plan. I called in to put a limit on so that it would not ever exceed my debit order amount. 6 months go by and everything goes off as norm. Last month this happened again. This month I was debited R887 for an R89 plan. ***!!! How please tell me did this happen. I want a refund and to cancel this horrible service with immediate effect.