Shocking interest charged on loans

I recently owed Capitec R23000 for a loan i took out in 2012, when i went to settle the amount was pushed up to 27000, and i delayed, after two months of paying 3512/month my balance remains to date over R26000, how can this be possible, other banks when you aske to settle gives a lesser amount/ discount but Capitec would rather add, and your amount does not decrease at all, after 5 years of paying-off the loan amount. what can i do about this.