Excessive Balance after 2 hours

Hi, I took out a personal loan of R40 000, the money was paid into my account at lunch time today. I just liked the loan account to my internet banking to find that the repayable balance is gone to R58 000.00 how did that happen? surely interest is added based on the daily outstanding amount and not a lumpsum. After 2 hours R18000 interest has been added.<br> <br> I called the call centre only to get told that they don't know how the amount is calculated.