Santander Consumer USA review: predatory lending

I got an auto loan with Santander USA on Dec 31st 2014. At the time I was working, but shortly after purchasing the car I was laid off. Once I secured new employment I did everything possible to get current and stay current however with they excessive charged I have not been able to catch up. My original loan amount was 21, 822, however as Oct 31, 2018 I owe 24, 621. I have paid this company over 15, 000 and nothing has gone to the principle everything is going to interest. When I have discussed this with Santander they said I would need to pay more than my monthly payment of 565.98 to see something go to the principle. They call me 3 to 4 times per day all times of the day and night. This company has defamed my character reporting incorrect information on my credit report. I have asked them to send me and itemize detailed statement in writing stating every payment and they have not only direct to the website. I believe Santander has violated my consumer rights with their predatory lending practices. I really do not know what to do