Wikia recently moved to a new contact system so I am not entirely sure which form is best for this case. However, it is definitely either this or this. By the way, referring to admin as staff can sometimes cause confusion. Although the two terms can be seen as interchangeable as far as general English is concerned, they are actually two distinct and different groups of users here on FANDOM. Admin are users who have, well, administrative rights on a particular wiki while staff are paid employees of Wikia. While staff can be admins, most admins are not staff.
If the issue is harassment and/or encouragement of violence, I would suggest using the second link.
No worries about the terms. I just thought I would bring it up in case you didn't know. There are a lot of wikis that use the two interchangeably so it is reasonable that some users don't think about the distinction when posting here. However, since this wiki is about getting help, the distinction is a bit more important on here.
Evidence of ToU violation is always a good reason to contact FANDOM staff. Assuming they agree it is a violation, they should act quickly. You can also discuss the issue with them via email after the initial report.
It's too bad, the new report form sometimes makes it harder to report.