Dealing with your lender or servicer: Student loan

My loan interest rate was approximately 12 % for the first two years, but the interest rate later changed to approximately 2 % in the middle of the repayment period. Because of this significant reduction in the interest rate, I expected that a much larger portion of my payments would be applied toward reducing the principal balance. However, after making approximately $6900.00 in payments on an original loan amount of approximately $14000.00, my principal balance has only decreased by approximately $130.00. I am requesting a complete explanation of how this was calculated, including how much of each payment was applied to interest versus principal before and after the interest rate changed. I believe the amount of principal reduction shown on my account does not appear consistent with the payments I have made and the lower interest rate that applied during part of the repayment period. I am requesting that Sallie Mae review my account for any possible servicing errors, incorrect payment allocation, or inaccurate interest calculations. I am fully aware of the predatory accusations in the past that Sallie Mae has been accused of when it comes to student labor or debt. I understand how interest works, but nothing about this situation. Makes sense nor is it fair. or professional