I cannot offer much useful advice because 1) You do not mention which state you live in, which may have laws protecting consumers with towed vehicles, 2) You do not say how much time elapsed between when you were quoted the $500 fee and when you went to retrieve the vehicle, 3) You do not mention why the vehicle was towed, 4) You do not mention the value of the vehicle or if it has a lien on it.
Because I know so little about your situation, I will recommend that you contact your county bar association and learn the name of an attorney in your area who has experience in consumer law. If you cannot afford an attorney, then ask the county bar association for the name of the local agency that assists low- or no-income people with legal issues. Make an appointment with a paralegal or attorney with that agency and bring all of the paperwork relating to the towing and the ownership of the vehicle to the meeting. Listen to your options, and act accordingly.
I hope this information helps you Find. Learn & Save.