Rule of 78 Auto Loan

State of California:
deceptively signed me up for rule of 78 loan! Purchased used auto, 1st time buyer w/ no credit history, dealer financed at 21% because I had no credit, i asked questions about the loan, dealer described it as if it were a simple interest loan (which at the time I didn't know what that was) he said no prepayment penalty, 36 month term. rule of 78 loan and it's implications never entered the description and the document I signed did not clearly state what it was, if it stated it at all. i did not find out what was going on untill my 4th payment, and I had been overpaying thinking i was saving myself money! i was cheated! they told me i was getting something other than what i was getting! people at other banks i talked to said they thought that no one could do that loan anymore! Do I have any legal recourse at all? help!