PHP - Problemas de login con hash

Código PHP:

$a = $_POST['nombre'];

$b = $_POST['username'];

$c = $_POST['email'];

$d =password_hash($password, PASSWORD_DEFAULT, array("cost"=>12));

$e = $_POST['celphone'];

$f = $_POST['img_profile'];

$g = $_POST['tipo_usuario'];

<?php

session_start();

?>

<?php

require_once("conec.php");

?>

<?php

 $contador=0;

if(isset($_SESSION["session_username"])){

// echo "Session is set"; // for testing purposes 

header("Location: index.php");

}

if(isset($_POST["login"])){

if(!empty($_POST['username']) && !empty($_POST['password'])) {

 $username=$_POST['username'];

 $password=$_POST['password'];

$query =mysql_query("SELECT * FROM login WHERE username='".$username."' AND password='".$password."'");

$numrows=mysql_num_rows($query);

 if($numrows!=0)

{

 $row=mysql_fetch_assoc($query);

 {

 $dbusername=$row['username'];

 $password=$row['password'];

 $dbnombre = $row['nombre'];

 $id = $row['cod_us'];

 $correo = $row['email'];

 $telefono = $row['celphone'];

 $tipo_usuario = $row['tipo_usuario'];

 $foto = $row['img_profile'];

 }

if($username == $dbusername && $password == $password)

{

 $_SESSION['session_username']=$username;

 $_SESSION['nombre_usuario'] = $dbnombre;

 $_SESSION['cod_us'] = $id;

 $_SESSION['email'] = $correo;

 $_SESSION['celphone'] = $telefono;

 $_SESSION['tipo_usuario'] = $tipo_usuario;

 $_SESSION['password'] = $password;

 $_SESSION['img_profile'] = $foto;

/* Redirect browser */ 

 header("Location: index.php");

 }

 } else {

$message = "Nombre de usuario ó contraseña invalida!";

 }

} else {

 $message = "Todos los campos son requeridos!";

}

}

?>

$nombre = $_POST['nombre'];

$passIngresado = $_POST['password'];

$sql = "SELECT nombre,pass FROM usuarios WHERE `nombre` = $nombre";

if (password_verify($pass,$hash)){

    echo 'el password es correcto';

}else{

echo 'pass incorrecto';

header('Location: index.php?err=1');

}

if(isset($_SESSION["session_username"])){

// echo "Session is set"; // for testing purposes

header("Location: index.php");

}

if(isset($_POST["login"])){

if(!empty($_POST['username']) && !empty($_POST['password'])) {

 $username=$_POST['username'];

 $password=$_POST['password'];

if (password_verify($password,$hash)){

    echo 'el password es correcto';

}else{

echo 'pass incorrecto';

header('Location: index.php?err=1');

}

$query =mysql_query("SELECT * FROM loggeous WHERE username='".$username."' AND password='".$password."'");

$numrows=mysql_num_rows($query);

 if($numrows!=0)

{

 $row=mysql_fetch_assoc($query);

 {

 $dbusername=$row['username'];

 $password=$row['password'];

 $dbnombre = $row['nombre'];

 $id = $row['cod_us'];

 $correo = $row['email'];

 $telefono = $row['celphone'];

 $tipo_usuario = $row['tipo_usuario'];

 $foto = $row['img_profile'];

 }

if($username == $dbusername && $password == $password)

{

 $_SESSION['session_username']=$username;

 $_SESSION['nombre_usuario'] = $dbnombre;

 $_SESSION['cod_us'] = $id;

 $_SESSION['email'] = $correo;

 $_SESSION['celphone'] = $telefono;

 $_SESSION['tipo_usuario'] = $tipo_usuario;

 $_SESSION['password'] = $password;

 $_SESSION['img_profile'] = $foto;

$hash = password_hash('123456', PASSWORD_DEFAULT);