Accept to be unjustly marked as a cheater, or submit to a 30-60 minutes interrogation where the teacher think you're guilty and you need to prove that you're innocent.

It's only an obvious choice if you have total faith that your teacher will be fair, which you might doubt if the situation starts with "You're a cheater unless you prove me otherwise". In the worse case scenario you'll be grilled for one hour and still be marked as a cheater because you didn't convince the teacher.