NCA rules flouted, 300% percent interest charged on overdue account

I defaulted on a revolving loan of R10000 that was opened in 2013 , which I resumed paying at R376 pm. I recently enquired about the balance and was advised it is at R41000, with interest charged more than R800 pm. That is more than 300% of the original loan. I was then referred to the branch, their exact words was that the account should have been charged off a long time ago and the system is being fooled by the payments hence continuing to charge interest although the payments are not making any difference to the balance. Is it legal to charge 300% interest ?