Complaint sub-issue: Don't agree with fees charged

My Father co-signed for a Student Loan in XX/XX/XXXX. The loan was via XXXX back, but was serviced through XXXX XXXX ( XXXX ). The exact loan amount borrowed was {$3300.00}. The terms and conditions of this loan was 120 payments at {$51.00}, so that the amount paid back for the borrowed funds was {$6100.00} over the course of 10 years per the promisary note ( see attached ). XXXX XXXX never had the correct borrowed loan amount from the start. XXXX XXXX stated that the original loan amount was {$6600.00}, which is completely false via the attached promisary note. XXXX XXXX basically doubled the original borrowed amount and added lots of interest to an amount that was never actually borrowed in the first place. XXXX XXXX increased my original loan amount by {$2800.00} without legal ground. I have been scammed by XXXX XXXX into paying thousand and thousands of unaccounted monies towards a loan, in which I only borrowed {$3300.00}. 
To make matters even worse, I have attached proof that for several years ( XX/XX/XXXX, XX/XX/XXXX, XX/XX/XXXX, XX/XX/XXXX ) several of the payments that I made were not even being applied to the balance. My payments were never applied to the principal, or the interest. My balance remained the same for YEARS because XXXX XXXX neglected to apply my payments properly. So I have over payed a ridiculous amount of money, on a falsified borrowed amount. Furthermore, for all of those years..I was forced to pay high interest on a bogus loan amount, and they were not applying my payments to the balance FOR YEARS. ( Attached is proof that my account balance remained the same for years ). Several of the attached documents you will see indicate that the original loan amount was {$3300.00} ... NOT {$6600.00}. 
I also have attached my credit report to prove that I have never had a late payment while paying this loan. The credit report shows that they were advised that the terms of this loan was 240 months with the original amount of {$6600.00}. This is completely FALSE, via the promisary note, along with other statements that show the agreement was made to be 120 payments at {$51.00} for 10 years ... with a total pay back amount of {$6100.00}. 
The repayment schedule ( see attached ) is more proof that the original loan amount was {$3300.00} and NOT {$6600.00} XX/XX/XXXX, I was advised that my loan was outsourced to AES ( American Education Services ). I did n't think anything could get worse, but it did. AES doubled my payment from {$56.00} to {$110.00}. XXXX with no warning. I called AES and I was told that I would have to pay {$110.00} until the loan is payed off in the year XX/XX/XXXX. The representative also stated that they had to go back and review all of my payment history, and determined that they had to " double my loan in order to make sure I had it paid off in the agreed amount of time ''. That is when I realized something was truly wrong. This was the turning point for me, and I demanded my promisary note and proof of payments made since XX/XX/XXXX ( see attached ). AES continued to send me a bunch of nonsense regarding a " deferment '' and a " forbearance '' on my loan ... none of which I initiated. XX/XX/XXXX, AES finally sends me a letter advising my of an increased rate. ( A little too late ) I called AES several times to resolve this issue, and was treated with nothing but disrespect. 
I decided the best thing to do was to cash in my XXXX and pay off this loan, so that I could dispute it. I did not want to dispute this loan while still open, because I do not trust AES. The fact they admitted that they " reviewed my payment history '' ..clearly they saw something wrong! Instead of doing the right thing ... AES went along with it and got greedy and doubled my payments. I hold AES even more responsible for this mess than XXXX XXXX. I have attached proof of payment, along with the paid in full letter. If my calculations are correct, I have overpayed on this loan by close to {$9000.00}.