Product: Student loan

In winter XX/XX/XXXX, I called my student loan provider Navient to get clarification on how my payments would be applied if I paid over and above my monthly required payment. I was told that I would be given the option to apply the extra money to my next payment or pay down the principal on my loan. I said I always wanted to have it applied to the principal and the representative told me I would have the option to select this when I made my payment on line. On XX/XX/XXXX, I went online to try to change my monthly auto payment to a higher amount than I was required to pay ( in order to begin paying off principal ). I was not able to change the auto payment amount online so I called into Navient. On the same day ( XX/XX/XXXX ), a Navient representative told me she could change the auto payment for me and confirmed that my next payment would be for the amount I specified ( about {$90.00} more than I was required to pay ). My next auto payment was scheduled for XX/XX/XXXX. On XX/XX/XXXX, I checked my account to confirm that the new amount had been paid. The amount had not changed from the minimum required amount. I  then initiated a one time payment for {$100.00} to go toward my loan, as I had originally requested. I was not given an option to apply it to principal. The following business day, XX/XX/XXXX, I called Navient to complain that my auto payment amount had never been updated. I again asked that they update my auto payment amount to allow me to overpay and pay off my principal faster. The Navient representative told me that it takes 14 days to process a request to change the auto pay amount. According to her, because I had not called far enough in advance, my request to increase the monthly amount I am paying was not changed. This is incorrect as I called 15 days in advance of my auto payment deduction. The Navient representative then confirmed that my monthly auto payment in XX/XX/XXXX would reflect the ~ {$90.00} increase I had requested on XX/XX/XXXX. On the same call ( XX/XX/XXXX ), I then told her that I had made the {$100.00} payment on XX/XX/XXXX but had not been given the option to apply it to the loan principal. She promised to manually go into the system as soon as my monthly payment had fully processed and apply the {$100.00} dollar payment to the principal of my loan with the higher interest rate ( as I requested ). On XX/XX/XXXX, I logged into my Navient account to verify that the {$100.00} had been applied to my principal. My Navient account showed that 100 % of my extra payment had been applied to interest, not principal as I had requested. On XX/XX/XXXX, I called Navient again to complain about the issue and get them to correct it. The Navient representative that I spoke to told me that because my {$100.00} payment had not been made on the exact day that my auto payment had been processed, it went to outstanding interest on the account. This directly contradicts what I had been told on my previous calls to Navient. The representative apologized and told me that the previous representatives had given me incorrect information. I asked to speak to a supervisor. She put me on hold and then told me that none were available. Then I requested her to have a supervisor call me back, as I was at work and could not sit on hold. She put me on hold again and then told me that she was unable to get approval to have a supervisor call me back. Navient is engaging in abusive and fraudulent practices, making it impossible for me to control where my extra payments go through their online portal. Then their representatives give me bad information and lie about how my payments are being processed. I understand that my monthly payments are applied to interest as well as principal. However, when I pay above the minimum payment amount, I should be able to apply it to the principal so that I can pay off the loan faster and pay less interest over the life of the loan. I should also be able to do this without four separate calls to Navient and there should be more transparency over how payments are applied.