Stop car places from charging thousands of dollars in interest for doing nothing that should be illegal

What's up with auto loans? I was told that within the time it would take me to pay the 10,000 dollars for my car the interest accrued would only be 150 dollars because I put down almost 3,000 and was gonna be paying 300 a month . I've completely paid my car off and there saying I still owe them over 9,500 dollars!!! Where did a loan come from nobody ever gave me any money I paid for the car which is a 2005 Hyundai accent. I would never pay 20,000 dollars for a car that came with no amenities it was a used hatch back it didn't even have mirrors under the visor or cruise control. I also had to pay for all the maintenance that came with a used car. Someone told me about a Kelly blue book value and it said brand new my car wasn't even worth 4,000 dollars so how is this possible?