How to explicitly disable a client?

Question

C++ / C#

I am writing a chat in WCF. There are administrators in the chat. In particular, their rights include kicking the client from the server. There is a list of clients, which in particular includes callback channels to clients. How do I explicitly disable the client? I can only simply remove the client from the connected list so that it does not receive any more messages. But he will not actually kick, he will continue to be in the main chat window. How can I make it break the connection?