Product: Student loan

My loan is a consolidation loan ... upon consolidation of several loans the final consolidation loan was split into 2 loans ( XXXX, XXXX ) ... at some point, Sallie Mae changed ownership and Navient is now the servicing company for the 2 loans in repayment ... 

I developed a strategy to make extra payments on principle and only apply them to one of the loans ( XXXX ) ... extra payments are made on the due date and applied to principle so that no interest is incurred This is addition to the regular auto-debit payment that occurs, which satisfies the required interest payment, then whatever is left over goes to principle However, because both loans ( XXXX and XXXX ) have the same due date, any payment recieved ( regular, or extra ) is split equally between the 2 loans.  Even when using Navient 's payment tool online that specifically allows the payor to allocate payment amounts to specific loans, Navient is still not honoring the payor instructions. Navient claims that the " system '' automatically distributes the extra payment equally to both loans. Navient also says that the only remedy for the payor in this situation is to call Navient after the payment posts and speak to a customer service representative to manually re-apply those payments as per the payors instructions. Navient also states on thier hard copy statment that the payor can write a letter of instruction for application of payment and send it with the payment. But this is only for payments sent in via check, which I do not do. I do auto-debit, because I am assuming that there is a financial incentive for using auto-debit and that is my preference. I feel that Navient is not honoring the payor instructions/request for payment allocation because the responsibility lies with the payor to call and have the payments manually changed, even after providing payment instructions using the payment scheduling online tool. However, the call back process was working and payments were being applied as per the payor requests. This was occuring until XXXX of XXXX. Upon checking my balance I noticed that Loan XXXX had increased significantly. Navient had reversed the extra payments on Loan XXXX, unbeknownst to me, from XX/XX/XXXX thru XX/XX/XXXX. Upon calling Navient, I was told that the payment due dates for both loans had been realigned and that was the reason for the reversals. I did not understand the line of reasoning as the payment dates have always been the XXXX of each month since I started repayment. I was never contacted about any changes that were needed or were going to occur. So after a lengthy phonecall XXXX and going over my account transactions line by line, the customer service representative didn't seem to understand what I was talking about. Navient assured me that the payments were going to be re-applied once again and that I should see the results within 24-48 hours. This never occured. These servicing companies are playing with thousands of dollars and couping thousands of dollars in interest because of these types of mistakes. They are couping many more thousands from customers that aren't as astute with their payments and accounts as I have been. In addition, Navient is re-negotiating the repayment terms, which are very inconsistent. For example, the repayment terms have been changed 3 times in 4 months, giving me a different autodebit amount each time. I have no way of budgeting the autodebit if I don't know what the amount is supposed to be. Attached is a summary of the amounts and dates of the payments in question