^^ou need video evidence in order to report a hacker. Upload the video to Youtube. Once you did that, you may report the hacker here: https://www.cubecraft.net/forums/report-a-player.24/ . Make sure to include the link to your video, username and offense. If it is a long video, include the seconds in which you can clearly see evidence of using a hacked client.
You might also want to read this: https://www.cubecraft.net/threads/player-reporting-guidelines-and-formating.136047/