Change Email Address PHP System Gives Success Notice But Email Doesn't change in Database [duplicate]

I have a system for users to change their email addresses. I get a success notice after submitting the form but the new email address doesn't show up in the database.

The Entire Code is below

<?php 
session_start();
if(isset($_SESSION['id'])){
if(isset($_POST['change_email_submit'])){
    require 'dbh.inc.php';
    $registerId = $_SESSION['id'];
    $registerUsername = $_SESSION['userId'];
    $oldEmail = htmlspecialchars(trim($_POST['OriginalEmail']));
    $newEmail = htmlspecialchars(trim($_POST['NewEmail']));

    if(empty($oldEmail)){
        header("Location:../change_email_address.php?error=EnterOriginaEmail");
        exit();
    }
    if(empty($newEmail)){
        header("Location:../change_email_address.php?error=NewEmailEmpty");
        exit();
    }else if(!filter_var($newEmail,FILTER_VALIDATE_EMAIL)){
        header("Location:../change_email_address.php?error=invalidEmail");
        exit();
    }else{
        $sql = "SELECT registerEmail FROM register WHERE registerId='$registerId' AND registerUsername='$registerUsername'";
        $query = mysqli_query($conn,$sql);
        $queryCheck = mysqli_num_rows($query);
         if($queryCheck > 0){
             if($row = mysqli_fetch_assoc($query)){
                 if($oldEmail == $row['registerEmail']){
                     mysqli_query("UPDATE register SET registerEmail='$newEmail' WHERE registerId='$registerId'");
                      header("Location:../change_email_address.php?update=success");
                exit();
                 }else{
                     header("Location: ../change_email_address.php?error=emailunavailable");
                     exit();
                 }
             }

         }else{
             header("Location:../change_email_address.php?error=noUser");
             exit();
         }
         }
}else{
    header("Location:../change_email_address.php");
    exit();
  }
}