Unable to kill tty root user connections

I have a Digi PortServer TS 4. Every time I telnet in it leaves a tty connection. Over time it builds up until I receive a message stating: Access denied, port maximum exceeded. I try to remove the previous connections by issuing the kill command and the following message is returned: Task(s) logged out. I then issue the who command and I see that the connection is still there. How do I keep the connections from stacking up?