Changing things in an email server, using an app, doesn't actually change things in the server, it only changes them in the app. Use the webmail page that the company should be maintaining - or ask the company email administrator to straighten out the server for you. (It can be a mess when the server isn't configured the way it's telling the client it's configured, and you do things that should never be done in the client just for that reason. The admin can go in there and rename, delete, anything you need - you can't.) And if there's no webmail page, ask the admin to put one up.
In the future, don't add, delete, rename, etc., folders in the client, use the webmail page. (And if you do, you might have to delete the email server from the client, then add it again, so that they synchronize. Again, this depends on how the server is set up. [IMAP was supposed to fix all that, but as long as admins are able to mess with the settings in the servers, it won't be fixed.])