Symfony未知数据库

I have an issue with symfony. when i execute this code

$quiz = new Quiz();
$quiz->setTitle('A quiz.');
$quiz->setAuthor('Alexandre');
$quiz->setContent("Blabla…");
$em = $this->getDoctrine()->getManager();
$em->persist($quiz);

Symfony show me this error

An exception occured in driver: SQLSTATE[HY000] [1049] Unknown database 'quiz' 

But if i try to create the database it says that the database exists

php bin/console doctrine:database:create
Could not create database `symfony` for connection named default
An exception occurred while executing 'CREATE DATABASE `symfony`':

SQLSTATE[HY000]: General error: 1007 Can't create database 'symfony'; database exists

And

php bin/console doctrine:schema:update --force
Nothing to update - your database is already in sync with the current entity metadata.

This is my app/config/parameters.yml file

# This file is auto-generated during the composer install
parameters:
    database_host: localhost
    database_port: ~
    database_name: symfony
    database_user: root
    database_password: ~
    mailer_transport: smtp
    mailer_host: 127.0.0.1
    mailer_user: null
    mailer_password: null
    secret: 43c1fdc9712102f8b9c3e33ed1c46befd3dae9ab

Thank you for your help

STEP

1. php bin/console doctrine:database:drop --force
2. php bin/console doctrine:database:create
3. bin/console doctrine:schema:update --force

Symfony doc http://symfony.com/doc/current/book/doctrine.html

You have bad configuration your database name is symfony already exist

put this configuration in your parameters.yml

parameters: 
    database_host: localhost
    database_port: ~ 
    database_name: quiz
    database_user: root
    database_password: ~ 
    mailer_transport: 
    smtp mailer_host: 127.0.0.1
    mailer_user: null 
    mailer_password: null 
    secret:
43c1fdc9712102f8b9c3e33ed1c46befd3dae9ab

Next execute in terminal project directory

php bin/console doctrine:database:create

If not have the entity quiz create this with command

php bin/console doctrine:generate:entity AppBundle/Quiz

Update your database

php bin/console doctrine:schema:update --force

Final step execute you method from controller to persist and flush object in table quiz from database quiz