student loan repayment....where is my money

I have had a student loan with standard bank for 4 years and as of last year I started paying back my loan...my repayment is over r4000 a month;on a loan that in December was sitting at R196,592.22 it is now two months later after paying over r8000 towards it,my total is a whopping r196,118.33.this is not even a r500 difference?? I want to know what is going on here because when I phone ur call center I just get moved from one department to another and at this stage I feel like I am being ******.