There is an icon in cPanel called "FTP Session Control", but this feature only works with ProFTPd. All of our servers run PureFTPd.
The only way you can terminate FTP connections is to have jailshell enabled, then use 'ps' to list the processes and 'kill' to kill the ftpd processes.
ps afux |grep ftpd
...
kill ####
...
kill ####
Be sure to replace #### with the actual PID you get.