If you cannot access either WHM and SSH with root user, you might want to try to run the SSH autofixer

You can try using the SSH autofixer that is built into the WebHost Manager. You can call it using the following URL:

http://your_server_ip:2086/scripts2/doautofixer?autofix=safesshrestart

Replace your_server_ip with the actual server IP address. This function will attempt to restart sshd with a very basic, default configuration, with sshd listening on port 22. If successful, this will allow you to log in and investigate and correct any problems in your sshd configuration (/etc/ssh/sshd_config).