Well, you can say that you knew it was unpaid but you didn’t realize you’d be doing something illegal if you accept an unpaid job where you provide an actual service where the employer makes money but doesn’t pay you minimum wage, and that for your college an unpaid internships ALSO needs to be “for credit” and meet educational value criteria, or be paid. So, if they say they won’t pay you, don’t go further - they were just trying to exploit you as the ultimate cheap (free) labor.