使用Composer找不到TwitterOAuth ...其他类工作正常，为什么不呢？

I am including the TwitterOAuth library as suggested on the site here

https://twitteroauth.com/

this is my composer.json

{
    "require": {
        "opentok/opentok": "2.2.x",
        "abraham/twitteroauth": "0.6.*",
        "facebook/php-sdk-v4" : "4.0.*"
    }
}

in my index.php file in codeigniter I have these lines

require_once './vendor/autoload.php';
use Abraham\TwitterOAuth\TwitterOAuth;

My Facebook library loads fine and everything is working, as is everything else included with composer

however in my controller when I try to post with this

  function post()
    {
        try {
            $to = new TwitterOAuth('key', 'secret', 'auth_token', 'auth_token_secret');

            $params     =   array('status' => 'Trial Post');
            $do_dm      =   simplexml_load_string($to->OAuthRequest('http://twitter.com/statuses/update.xml', $params, 'POST'));
        }
        catch(Exception $o ){
            print_r($o);
        }
    }

I get the error that Class 'TwitterOAuth' not found

I have been digging for a while and don't get how this is not working.. Can anyone help?