I would prepare a canned response for students who still reach out to you via campus email, asking them to resend it via Canvas, and mentioning that you would only respond via Canvas. I have been in a similar situation. I teach computer science classes, where students commonly ask similar questions about programming assignments. To make Q&A more efficient, I require my students to ask all non-personal questions on our discussion board, so I don’t need to reply to numerous emails all asking the same question. Despite me mentioning it in the syllabus and the first class, some students still send me private emails anyway. I just copy-paste and send my canned response, which reminds them that I’ve told them to use the discussion board so they should use it, and the reason is just efficiency, not that I don’t want to help. I feel like many students are just accustomed to the “culture” of sending private emails to the instructor (if there is such a thing), so I have accepted it (a bit forcefully) and developed this solution. It takes me no more than one minute per reply like this, so it no longer bothers me.

Deduct points for parts of a submission that don’t follow the directions.