I have a student who has handed in a term paper from another class, only changing the title page, and he claims that he only put the due date for the current course's term paper on the cover sheet of the old term paper to remind him of when the new term paper was due. He claims he was then cutting and pasting (appropriately, of course) between the old paper and the new paper and must've gotten the two files mixed up. Of course, the "wrong" file (old term paper with new due date) was "accidentally" uploaded to our learning management system and he did submit the "correct" file two days later (that was extremely poor quality), but only after I pointed out the problem to him.
Now he is claiming I am unreasonable because I don't believe him and have failed him for the course. We are about to go to a grade appeal at the department level. I was wondering if everyone on here could provide suggestions for why it is reasonable to stick to my decision, despite the student arguing very vigorously that I'm unreasonable, unfair, and even irrational for not believing this was "just an honest mistake". (Given my university's fondness for "student friendly" I may not be supported very vigorously by the committee.)
Any help is greatly appreciated.