If you have been griefed, don't panic. All grief is easily revertable. Do not attempt to repair the grief yourself as that makes it more difficult for staff. These are the steps to take to recover your build and items:
Claim your land. This will prevent more grief on your land. Land must be claimed in order for staff to rollback grief. For help on claiming, see this page.
Use the Minecraft command /discord link and follow the instructions to link your Minecraft account to Discord.
Create a ticket by reacting in the #support Discord channel. This will open a new private Discord channel for you to post your issue.
In the new channel, explain that you have been griefed and provide the coordinates of the grief. You can obtain your coordinates with the command /coords. It could also be helpful to provide a time interval for when the grief happened, name a few blocks or items that were taken, and name any players who you know were involved.
Patiently wait for staff to restore the grief. It should take a few hours at most.