中止不适用于$ .get

Question

I am using jquery. I write a script where user A create chatwindow/chatbox for chatting user B, when window opened $.get method start sending request to server for check new message. My code works perfectaverything... but I want when user A close chatbox of user B then $.get shouldn't be send request to server.

Here is my $.get function that send request to server for check new request:

function getMessages(sender, receiver,receiverName, Clbk) {
    $.get('chat.php',
        { sender: sender, 
            receiver: receiver
        },
        function(response) {
        //console.log(response);
        if(response.success) {
            var html = '';
            var messages = response.messages;
            for(var m in messages) {
                var message = messages[m];
                var senderId = message.sender;
                var receiverId = message.receiver;
                var timestamp = message.timestamp;
                var body = message.body;
                //var msgId = message.msgId;
                html += '<p><b>'+((senderId == sender)?'ME':receiverName)+'</b>: '+body+'</p>';
            }

            $('.usermsg'+receiver).html(html);
        }

        if(Clbk) {
            //console.log(Clbk);
            Clbk();
        }

    });
}

When I call this function code(when user click on User B it start sending requests):

callback = function () {
    setTimeout(function(){
        getMessages(sender, user_id, username, callback);
    }, 3000);
};
getMessages(sender, user_id, username, callback);

This code is when user A close window for chatting User B:

**$('#windows').on('click','.cls', function(){
    **getMessages(sender, user_id, username, callback).abort;**
    $(this).parent().parent().remove();
});**

How can I stop sending request to the server?