Symfony - Event not being dispatched

This is the first time ever I am working with creating custom event dispatcher and subscriber so I am trying to wrap my head around it and I cant seem to find out why my custom event is not being dispatched.

I am following the documentation and in my case I need to dispatch an event as soon as someone registers on the site.

so inside my registerAction() I am trying to dispatch an event like this

$dispatcher = new EventDispatcher();
$event = new RegistrationEvent($user);
$dispatcher->dispatch(RegistrationEvent::NAME, $event);

This is my RegistrationEvent class

namespace AppBundle\Event;
use AppBundle\Entity\User;
use Symfony\Component\EventDispatcher\Event;

class RegistrationEvent extends Event
{
    const NAME = 'registration.complete';

    protected $user;

    public function __construct(User $user)
    {
        $this->user = $user;
    }

    public function getUser(){
        return $this->user;
    }

}

This is my RegistrationSubscriber class

namespace AppBundle\Event;    
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\FilterResponseEvent;
use Symfony\Component\HttpKernel\KernelEvents;

class RegistrationSubscriber implements EventSubscriberInterface
{
    public static function getSubscribedEvents()
    {
        return array(
            KernelEvents::RESPONSE => array(
                array('onKernelResponsePre', 10),
                array('onKernelResponsePost', -10),
            ),
            RegistrationEvent::NAME => 'onRegistration'
        );

    }
    public function onKernelResponsePre(FilterResponseEvent $event)
    {
        // ...
    }

    public function onKernelResponsePost(FilterResponseEvent $event)
    {
        // ...
    }
    public function onRegistration(RegistrationEvent $event){

        var_dump($event);
        die;

    }

}

After doing this, I was hoping that the registration process would stop at the function onRegistration but that did not happen, I then looked at the Events tab of the profiler and I do not see my Event listed their either.

What am I missing here? A push in right direction will really be appreciated.

Update: I thought i need to register a service for the custom event so I added the following code inside services.yml

app.successfull_registration_subscriber:
    class: AppBundle\Event\RegistrationSubscriber
    arguments: ["@doctrine.orm.entity_manager"]
    tags:
        - { name: kernel.event_subscriber}

Inside the Event tab of profiler I do see my custom event being listed but it still does not dispatch.

By creating your own EventDispatcher instance you dispatch an event that can never be listened to by other listeners (they are not attached to this dispatcher instance). You need to use the event_dispatcher service to notify all listeners you have tagged with the kernel.event_listener and kernel.event_subscriber tags:

// ...

class RegistrationController extends Controller
{
    public function registerAction()
    {
        // ...

        $this->get('event_dispatcher')->dispatch(RegistrationEvent::NAME, new RegistrationEvent($user););
    }
}