You can try to appeal your ban here : https://appeals.cubecraft.net/.
And if that didn't work , try to contact the staff member that banned you by starting a conversation with him/her. Also, make sure not to spam their profile , some staff members may find that annoying.
And if that didn't work , try to contact the staff member that banned you by starting a conversation with him/her. Also, make sure not to spam their profile , some staff members may find that annoying.