In Washington, the current limit on interest rates is 12%. Loans that charge interest rates in excess of the limit are usurious. However, there are many exceptions depending on the transaction and the parties involved. I am posting some links below that I hope will explain how these laws work.
As far as what you can do, usury is a defense to nonpayment of a loan. In other words, if the lender sues you to collect, you may be able to avoid some or all of the amount due. Although the law does not give you any direct recourse against the lender, you may be able to renegotiate the loan.
Because the usury laws can be very fact-specific, you should consult with an attorney to obtain advice that addresses your particular circumstances. Good luck.