How to limit replies to 1 API Call?

I'm making a Q&A twitter bot w twitter api using direct messages, my problem is each time a user ask a question, after a while, the bot start to response twice the same answers. Is there a way to limit each response to 1 API Call?

here my code:

stream.on('direct_message', function (eventMsg) {
    var msg = eventMsg.direct_message.text;
    var screenName = eventMsg.direct_message.sender.screen_name;
    var msgID = eventMsg.direct_message.id_str;

    if (screenName === ‘MyBotExample) {
        return callbackHandler(msgID);
    }

    else if (msg.search(‘Hi’) !== -1 ) {
        return T.post('direct_messages/new', { 
            screen_name: screenName,
            text: 'Hey, what can I do for you?'} , function () {
            callbackHandler(msgID);
        });
    }

    else {
        return T.post('direct_messages/new', {
            screen_name: screenName,
            text: "I don't know "
        }, function() {
            callbackHandler(msgID);
        });
    }
});

Thanks!

via Isaac