Product: Payday loan, title loan, or personal loan

I received a Pre-Approved check in the mail in XXXX and after a few weeks elected to take the offer. The check was for {$25000.00}. After some contemplation, I concluded I wanted to use a lower amount. I called the PENFED Credit Union and conversed with a Rep which initially informed me I was unable to decrease the loan amount. She ultimately told me she could withdraw $ XXXX which was arranged at that time. I was advised that my first payment date was XXXX of XXXX. 
Since that date, I called the bank maybe 3-4 separate times about different questions and it was never mentioned I was late on an installment, etc. 
Moving forth to XXXX of XXXX I log in to make a payment ... the {$250.00} payment was processed. 
XX/XX/XXXX arrives and I logon to begin my next installment and noticed my payment amount was {$640.00}, of course, that was surprising. I instantly called the bank to obtain transparency on why the amount increased. Hold time was extreme! So I called the following day XX/XX/XXXX and spoke to XXXX XXXX, she explained that she recognizes where the mistake occurred and that once the $ XXXX was placed back in the account the loan should have been revised ... because it charging me as if I have the $ XXXX. Of course, it wasn't prepared the route shes insinuating it should've been prepared. She mentioned she needed to communicate with her supervisor to find out the most reliable way to get this solved and would call me back within 2 days. I actually didn't hear back from her ... After a few weeks of not hearing back, I proposed an email message requesting someone to reach out to me. She ( XXXX ) called me back on Monday, XX/XX/XXXX, and explained she " dropped the ball '' and really forgot to get the information needed to settle my concerns. 
She convinced me she was reaching out to her manager that day and would call me back the following day. 
Today XX/XX/XXXX she called me saying that she was sorry, and everything has been out of wack and she heard back from the supervisor XXXX XXXX which informed her via email that it was nothing she could do, except waive {$1000.00} of the interest on the account. She also declared that I allowed to much time to pass by before contacting the Bank with my concerns. I reminded her that I immediately called so I was confused about the time-lapse she was stating. 
XXXX essentially said she wasn't certain what else to do, and she could bring this up to the board members as I mentioned filing a compliant ... she understood where I was coming from, but the decision wasn't hers to make. 
She also said she would have her Supervisor to contact me and perhaps she would be able to make the modifications after speaking directly to me. 
Of course, I was shocked and now unsettled that I'm obligated to make payments as if my loan amount is {$25000.00} with a 17.99 % APR. The interest solely is ridiculous for my credit score. I was told the APR couldn't be adjusted either. XXXX loans APR 's are being reduced based off a person 's credit score. I didn't understand why this wasn't an option with XXXX. 
This complete loan process was arranged wrong and I sense I was deceived into repaying a larger amount for bank advantages. 
That's outrageous, to say the least.