Greedy institution.

what kind of an institution is this? I registered with Unisa last year, second semester I registered five (modules) and in the process I cancelled two (2) because of the work load. when I checked my statement in December in order for me to make payment , the money due to unisa was R4180.00, I then paid R3100.00 and remained with an outstanding amount of R1080.00. To my surprise this January when I checked my statement it reflected that I now owe them R2080.00 and when I enquired they said the R1000 they added on fees its the interest accumulated. so I am asking myself so much interest for an educational institution. what percentage did Unisa use to calculate the interest added? Unisa is a **** and they are robbing us our right to education. Now im stuck I don't have money to register because the R1000.00 I thought im going to use to register for this Semester was used to pay for the interest they charged me and I felt I was forced to pay it because I wanted my results.