Very bad service and lack of knowledge.

I am so upset with Nedbank for the incorrect information given to me when I got my sister a student loan. I was a contract with a fixed capital that I would have to pay for 18 months as the Surety, All of sudden I am been told that I have to pay the interest until she is done with school. she is studying medicine, so I am basically paying the interest for the next 5 more years and according to my calculations I would have paid the total loan amount. Which is completely ridiculers because it is going against the contract...Total *******