Find anwer here: http://forums.androidcentral.com/samsung-galaxy-note-2/264604-cant-change-data-usage-cycle-anymore.html
Mobile Data must be on, WiFi must be off.
Find answer here:
http://forums.androidcentral.com/samsung-galaxy-note-2/264604-cant-change-data-usage-cycle-anymore.html
Mobile data must be on, WiFi off