An organization plan is cancelled by deleting the organization. If you would prefer, you can choose to pause a subscription instead of cancelling so you can return in the future. 

1. Click on the "..." to the right of the Organization name in the groups browser drop down. 

2. Choose Organization profile

3. Click the Delete this organization button

Note: Prior to deleting an organization, you may want to export all of the group members and any information collected from them in the Members pane.