Symfony 2.8 injecting twig

Pre-note: I am learning Symfony from a Drupal 7 background.

I have created a custom model (although I think they are called services in Symfony from what I have read), and would like it to render an array via twig into a variable.

I found this link, and thought that this injection approach would do the trick: http://symfony.com/doc/2.8/service_container.html

Sadly, I and up with the below error:

Type error: Argument 1 passed to AppBundle\Model\Newsletter::__construct() must be an instance of AppBundle\Model\Twig_Environment, none given, called in /home/dan/working_files/symfony-playground/src/AppBundle/Controller/DefaultController.php on line 130

So, I am wondering what is an acceptable approach so I can use twig within my custom model/service/class?

If it is of use, here is some of my code for reference:

services.yml

services:
    appbundle.newsletter:
        class: AppBundle\Model\Newsletter
        arguments: ['@twig']

src/AppBundle/Model/Newsletter.php

namespace AppBundle\Model;

class Newsletter
{
    private $twig;
    public function __construct(Twig_Environment $twig)
    {
        $this->twig = $twig;
    }
}

Calling my model

$newsletter = new Newsletter();