swiftmailer slim framework

Bonjour,

Voila je rencontre un petit problème avec mon code.
Voici l'erreur:
Slim Application Error
The application could not run because of the following error:

Details
Type: Error
Message: Call to undefined method Swift_SmtpTransport::newInstance()
File: C:\wamp64\www\slim\app\Commander\dependencies.php
Line: 68

Voici ma page dependencies.php

<?php

use Respect\Validation\Validator as v;

v::with('App\\Validation\\Rules\\');
$container = $app->getContainer();
$container['debug'] = function () {
    return true;
};

// Service factory for the ORM
    $capsule = new \Illuminate\Database\Capsule\Manager;
    $capsule->addConnection($container['settings']['db']);

    $capsule->setAsGlobal();
    $capsule->bootEloquent();

$container['db'] = function ($container) use ($capsule) {
    return $capsule;
};

// toggle mode: development -> production
$container['dev'] = function ()
{
  return true;
};
$container['csrf'] = function ($c) {
    return new \Slim\Csrf\Guard;
};

$container['flash'] = function ($container) {
    return new \Slim\Flash\Messages;
};

// instanciation du rendre des vue twig
$container['view'] = function ($container)
{

    $view = new \Slim\Views\Twig(__DIR__ .'/../../app/Templates',
    [
        'cache' => $container->dev ? false : (__DIR__) . '/../tmp/cache/twig',
        'debug' => $container->dev,
        'auto_reload' => $container->dev
    ]);
    if ($container->dev) {
      $view->addExtension(new Twig_Extension_Debug());
    }
    // Instantiate and add Slim specific extension
    $basePath = rtrim(str_ireplace('index.php','', $container['request']->getUri()->getBasePath()),'/');
    $view->addExtension(new \Slim\Views\TwigExtension($container['router'], $basePath));
    $view->addExtension(new \App\Extensions\CsrfExtension($container['csrf']));
    $view->getEnvironment()->addGlobal('flash', $container->flash);

    return $view;
};
// mail sender (swift_mailer)
$container['mailer'] = function($container)
{
  if ($container->debug)
  {
    $transport = Swift_SmtpTransport::newInstance('localhost',1025);
  }else {
    $transport = Swift_Transport::newInstance();
  }
  $mailer = Swift_Mailer::newInstance($transport);
  return $mailer;
};
...

public function postContact(RequestInterface $request, ResponseInterface $response){

    $message = Swift_Message::newInstance('Message de contact')
                ->setFrom([$request->getParam('email') => $request->getParam('name')])
                ->setTo('contact@monsite.fr')
                ->setBody("Un email vous a été envoyé :
            {$request->getParam('content')}");
            $this->mailer->send($message);
            $this->flash('Votre message a bien été envoyé');
            return $this->redirect($response, 'contact');

  }

Merci pour votre aide