Symfony3创建服务错误文件，但不在其中

This is getting me crazy. I know the answer will be stupid but around 1 and half day on this I need to ask, English isn't my native language so be patient please. First of all I'm trying to write a simple service but continuously getting the error

The autoloader expected class "AppBundle\Services\Helpers" to be defined in file "C:\xampp7.1.7\htdocs\curso-fullstack\vendor\composer/../../src/AppBundle\Services\Helpers.php". The file was found but the class was not in it, the class name or namespace probably has a typo.

on my services.yml file I got this

app.helpers:
  class: AppBundle\Services\Helpers
  arguments:
      - ["null"]

to define the service

my folder structure is src/AppBundle/Services/Helpers.php where I got the service class as follow

<?php
namespace AppBundle\Services\Helpers;

class Helpers {
    /* Funcion encargada de devolvernos un objeto json */
    public function jsonTemplate( $data ) {
        $normalizers = array( new GetSetMethodNormalizer() );
        $encoders    = array( "json" => new JsonEncoder() );

        $serializer = new Serializer( $normalizers, $encoders );
        $json       = $serializer->serialize( $data, 'json' );

        $response = new Response();
        $response->setContent( $json );
        $response->headers->set( "Content-Type", "application/json" );

        return $response;
    }
}
?>

Change the namespace to this:

namespace AppBundle\Services;

instead of this:

namespace AppBundle\Services\Helpers;

You have to change namespace of class Helpers:

namespace AppBundle\Services;