在服务中使用存储库

I'm trying to access a repository from a service, the repository works perfectly, I can use it from a controller, but not from a service.

Basically I have the following code:

namespace App\Service;

use App\Entity\Credencial;
use App\Repository\CredencialRepository;

use Doctrine\Bundle\DoctrineBundle\Repository\ServiceEntityRepository;
use Doctrine\Common\Persistence\ManagerRegistry;

class Authentication extends ServiceEntityRepository
{
    public function __construct(ManagerRegistry $registry)
    {
        parent::__construct($registry, Credencial::class);
    }

    public function auth(string $key): string
    {
        $qb = $this->createQueryBuilder('c')
            ->andWhere('c.credencialKey = :key')
            ->setParameter('key', 'teste_key')
            ->getQuery();

        $credencial = $qb->setMaxResults(1)->getOneOrNullResult();
        return $credencial->execute();
    }
}

This is the last thing I tried, I was trying to query without the repository, but didn't work either.

I didn't touch the service.yaml or other config file.