Santander Consumer USA Consumer Loan Complaint

Santander Consumer USA Consumer loan department,

Vehicle loan Managing the loan or lease Florida

I purchased a car over two years ago and Santander Consumer USA financed the loan. I was not aware at the time that the interest rate was over 16 %. This high interest rate raised my car payment to well over $640.00. At the time of purchase I was able to make the payment but after being demoted and pay rate being decreased, I contacted Santander for help and they offered me an auto loan modification for six months which lowered my car payments to a little over $380.00 and I was able to make the payments for that time. I decided to seek another car and attempted to trade the car they financed in for a cheaper and more affordable car payment only to find out that the pay off for this vehicle was over $30000.00. I was told by the dealer that I was victim of a predatory auto loan where all of my payments were only applied to interest and not principal. I am trying to find out if this type of loan is legal and is there anything I can do to get them to lower my auto payments. The dealer stated the large payoff amount is the reason why I can not get into a cheaper car and why my principal payments are not going down? I have made payments in the amount of over $12000.00.