Thank you for your frantic phone call today. You are correct. The class you were registered for just "magically" disappeared. We were hoping you would never notice that you were administratively dropped from the class because you failed the prerequisite course.
You know, that's the funny thing about prerequisite courses. You not only have to take the prerequisite, you actually have to PASS the prerequisite. I know that it is unbelievably unclear and our expectations are so muddled. I'm sure the email we sent you two weeks ago stating "You do not have the prerequisite for this course. You are being dropped from this course" was incredibly confusing. I don't know how you should have been able to gather that you were administratively dropped.
But again, you are right. It did just "magically" disappear. Unfortunately, I do not have a magic wand and so cannot make it magically reappear.