Problems with PHP: password_verify ()

I have a problem with password_verify() , apparently it is not comparing the password and the hash, no matter what I do it always results in error, my code is as follows:

try{
    $base = new PDO("mysql:host=localhost; dbname=usuarios","root","");
    $base->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $sql="SELECT * FROM login WHERE usuario= :usuario";

    $resultado=$base->prepare($sql);

    $user=htmlentities(addslashes($_POST["userName"]));
    $password=htmlentities(addslashes($_POST["userPassword"]));     

    $resultado->execute(array(":usuario"=>$user));

    $registro=$resultado->fetch(PDO::FETCH_ASSOC);

    if(password_verify($password, $registro['password'])){
                  if(isset($_POST["checkbox"])){

                                    setcookie("nombre_usuario", $_POST["userName"], time()+86400);                  

                                    session_start();
                                    $_SESSION["sesion"]=$_POST["userName"];
                                    header("location:usuarios_registrados.php");

                                }else{
                                        session_start();
                                        $_SESSION["sesion"]=$_POST["userName"];
                                        header("location:usuarios_registrados.php");
                                        }     
        }else{
                echo "Error";
            }

    }catch(Exception $e){
        die("Error " . $e->getLine() . $e->getMessage());

        }

I tried using:

  

password_verify ($ _ POST ["userPassword"], $ registration ['password'])

This is how users register:

$usuario= $_POST["user"];
$contrasenia=password_hash($_POST["password"],PASSWORD_DEFAULT);

try{
    $base=new PDO('mysql:host=localhost; dbname=usuarios', 'root', '');

    $base->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $base->exec("SET CHARACTER SET utf8");      

    $sql="INSERT INTO login (usuario, password) VALUES (:usuario, :contrasenia)";

    $resultado=$base->prepare($sql);        


    $resultado->execute(array(":usuario"=>$usuario, ":contrasenia"=>$contrasenia));     


    echo "Registro insertado";

    $resultado->closeCursor();

}catch(Exception $e){           

    echo "Línea del error: " . $e->getLine();

}finally{

    $base=null;

}

but it still does not work.