A life time 5year loan!!

5 year revolving credit loan. Been paying off for 6 years. Almost same amount outstanding. Reported error 3 times. No results no feedback. Calls are being logged and closed nexy day. Clearly system error on calculations. Interest, life insurance and rates are not consistent and more than 50% of payment. A 5 year loan of R20000and only R5000 paid....???? Consultans are no help. I have a personal and business account at STB. NOT A HAPPY CUSTOMER