Product: Student loan

I sent in a large check ( {$66000.00} ) to Navient with a letter with XXXX sentences on how I wanted the payment handled. It was to be applied to pay off XXXX specific ( high interest ) loans in their entirety. I specified by loan # which loans they were & also that it was to pay them " in their entirety- both principal as well as current interest ''. When the letter was received XX/XX/2016, the instructions were completely ignored & I have made several ( more than 8 ) phone calls & spoken to the loan provider as well as supervisors in the billing department. All of them assure me that they understand & the payments will now be applied correctly as per my letter. The payment has yet to be properly applied. Every single representative & supervisor I have spoken to has claimed that they will be " going back retroactively '' to apply the payment to the loans so that I am paying the principal & interest that was on the loan XX/XX/XXXX & not what has accrued since they have received the payment. On XXXX XXXX, I received a letter from Navient stating that XXXX of my loans has been paid off. I went back into my account to see why the letter did not state that XXXX of my lans had been paid off. The remaining loans that were supposed to be paid are still accumulating interest, though most of the balance has been removed. The loans are not supposed to be doing that. They were supposed to be paid in full as per my letter & the instructions contained within it. They are intentionally NOT applying the payment correctly in order to charge me interest on loans that were suppsed to be closed over 1/3 of a year ago. I spoke to supervisor, XXXX XXXX last Friday, XXXX XXXX, & he assured me that he was going to personally see that e issue was taken care of. He called me later that same day, told me the loans were correctly paid & that the changes would reflect by the morning of the following day ( XXXX XXXX ). I gave it a few extra days " just in case '' & checked my account this morning ( XXXX XXXX ) & found that the loans were again, not up to date & that for the 8th time, my payment had not been properly applied. I did, however receive a letter in my account that the payment dates were changed- which was a surprise, because at no time did I ever discuss such a matter with the supervisor, XXXX XXXX . Today, XXXX XXXX, I again called Navient & spoke with the representative who ( of course ) assured me & said they would get the matter resolved. She told me that she walked over to XXXX 's office & personally spoke with him & he acknowledged that there was an error on my account. It appears to me that Navient is intentionally applying my payment incorrectly so that they can continue to attempt to charge me interest on loans that have lieterally already been paid for. They have received the money, they have cashed the check, and they are refusing to close the loans that had been paid for nearly 5 months ago, all while still charging me interest on all but XXXX of them. The dates that I have documented that I called Navient & spoke to a representative who assured me every single time that they understood the issue & would resolve it were as follows : XXXX XXXX, XXXX XXXX, XXXX XXXX, XXXX XXXX, XXXX, XXXX XXXX, XXXX XXXX, XXXX XXXX, XXXX XXXX, and XXXX XXXX, ( all in 2016 ). I desperately need help resolving this issue since the loan provider is refusing to apply my payment to the loans- further charging me interest on the loans that they have accepted the money for, and not closing said loans, which is in addition to being illegal, is also adversely affecting my credit.