Yes, you can be: you may have committed one or more crimes, such as "theft of services" (getting them to fix your car, then not paying for it). If you feel they have been improperly holding onto your car--taking too long to fix it; charging more than you had agreed to pay and refusing to return the car until you pay; etc.--then you can go to court and file a lawsuit seeking the return of the car and potentially monetary damages (compensation), too; that's the way to get the car back if they've done something wrong. On the other hand, if they have done what there were supposed to and are not acting improperly, to legally get your car, pay them or work out a payment plan with them.