*******, robbing you silently with "miscalculations"

Discovery are generally a good company but since i shifted from my broker it was chaos. I cancelled my medical aid when I resigned from my school in South Africa, I was given an amount to pay for cancelation. All of a sudden after I paid I suddenly owe more. Then when queried it was about a miscalculation of dates and ******* like that, but the amount was calculated on the day I called or queried. How i there a miscalculation suddenly bringing other days into account which was never mentioned when I queried. Now I am being annoyed with emails, how must I pay I don't live there anymore and I cannot do international transfers. Your service is poor you are sharks. How does it become my problem if your team made a mistake, why must I be held liable for your mistakes. Now you giving me stress and issues because you handed me over to a credit authority or because your team made a mistake. Your team should be held liable for your own mistakes. you can't make me pay and when I leave SA you want more money from me. That is dishonest especially if you were wrong. Explain this to me in a good well written descriptive email. please share all details why i am liable to pay because of a fault on your side.