In the Settings option of Nelio Content you can delete a social profile from Nelio Content. Doing so, nobody can schedule new social messages nor any scheduled message will be published. However, Nelio Content will still have access to that network, since you can have other websites that do have configured that profile and thus need to post messages on it.
To completely delete Nelio Content permissions on Twitter, go to your Twitter account (in Twitter’s website) and select Settings (on the menu under your picture). On this new window, go to the Apps tab to see the list of apps that have access to your account.
Click on the Revoke access button next to Nelio Content, and the permissions will be revoked. Of course, you can always return to give Nelio Content access to Twitter.