Double jeopardy applies to a court of law, not to school discipline.

You have spelled out consequences for not following band expectations in your handbook that the student and parent both signed and agreed to, and that your admin approved.

Follow the handbook.

That being said, where is the kid going to go? They can't get a schedule change at this point in the semester. They've already lost credit in both classes. Figure out this solution before you fight this battle.