Undefined offset : 1 error on render controller Symfony - symfony

Question

I am stuck with a problem.
I have a controller in my Symfony 2.8 project named 'AchievementController'. which I put inside a folder named 'Registration'. I have a action named listAction which use to list all achievements. So my folder structure to controller is
AppBundle > Controller > Registration > AchievementController
I am using a file named list.html.twig to list all achievemets. I am planning to use render controller method to render listAction on another twig named new.html.twig. And my twig is placed at
AppBundle > Resources > views > Registration > Achievements > list.html.twig and
AppBundle > Resources > views > Registration > Achievements > new.html.twig.
My problem is when I used render controller method I got an error
"An exception has been thrown during the rendering of a template ("Notice: Undefined offset: 1") in AppBundle:Registration/Achievement:new.html.twig"
I have search a lot but every post tell to do the same way I did (I believe), but not working. And I am stuck there. I am attaching my action and twig. Do I want to set some configuration? What mistake I have done?? I have check the same in other projects and it works fine. So I'm confused. (And when I use a folder structure AppBundle > Controller > AchievementController and change code for this, it works fine. Simply it feels like a escape slash problem. But I didn't get any way to fix it.)
new.html.twig
{{ render(controller('AppBundle:Registration/Achievement:list')) }}
listAction
$em = $this->getDoctrine()->getManager();
$entities = $em->getRepository('AppBundle:Registration\Achievement')->findAll();
return $this->render('AppBundle:Registration/Achievement:list.html.twig', array(
'entities' => $entities,
));
list.html.twig
{% if entities %}
--------
--------
{% endif %}
Thanks for every answers.
I have used yml method to generate bundle.
I am attaching my action and controller here. (Removed other actions in controller)
<?php
namespace AppBundle\Controller\Registration;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use AppBundle\Entity\Registration\Achievement;
use AppBundle\Form\Registration\AchievementType;
class AchievementController extends Controller {
public function listAction() {
$em = $this->getDoctrine()->getManager();
$entities = $em->getRepository('AppBundle:Registration\Achievement')->findAll();
return $this->render('AppBundle:Registration/Achievement:list.html.twig', array(
'entities' => $entities,
));
}
}