I have completed iTheorie, but unfortunately I failed my theory exam.
That's unfortunate. Please check carefully whether you have already activated the refresher course or not. Within iTheorie, you can initially take all 50 practice exams once. However, if you unexpectedly fail, you can activate the refresher course once more free of charge. All 50 practice exams will then be available again. You can use the refresher course for a maximum of 3 months, so make sure you schedule a new exam in time.