Citibank Student Loan Complaint

Citibank Student loan department,

Non-federal student loan Dealing with my lender or servicer Ohio

I took - private loans from Citi Bank between -/-/--/-/-. I was an international student then so I was not eligible for federal aid. - of the - loans were sold to -, - continues to be with Citi. This - ( originally a - $ loan ) I still have with Citi has a 6.5 % interest rate. I have been making regular payments since I finished graduate school. On addition, whenever I can, I have made payments towards my principle. However, I just realize that the math does not add up. For instance, though I made a payment of - $ towards my principle -/-/-, my balance is still way above - - How could that be given that my original loan was - - I have stayed on top of my monthly payments, and I have made other additional payments, clicking the box that says apply towards principle ''? Thank you for your help!