Getting error "Uncaught Error: Call to undefined method mysqli_stmt::fetch_array()", while checking existing email and mobile [duplicate]

Question

I'm trying to register a user but first check if mobile and email already register. All other validations are done by jQuery and a request is sent by ajax to this PHP page. Everything is working fine if there is a new user, but that existing email and mobile checking part is not working. I'm getting this error -> "Uncaught Error: Call to undefined method mysqli_stmt::fetch_array()".some one please help.

<?php
require('db_connection.php');
if($_SERVER['REQUEST_METHOD']=="POST"){
    $name=$_POST['name'];
    $email=$_POST['email'];
    $mobile=$_POST['mobile'];
    $password=$_POST['password'];
    $hashed_password = password_hash($_POST['password'], PASSWORD_DEFAULT);
    $sql = "SELECT `user_email`,`user_mobile` FROM `users` where `user_email` = ? OR `user_mobile` = ? LIMIT 1";
    $stmt = $conn->prepare($sql);
    $stmt->bind_param("ss",$email,$mobile);
    $stmt->bind_result($email,$mobile);
    $stmt->execute();
    $stmt->store_result();
    if($stmt->num_rows > 0){
        $row = $stmt->fetch_array(MYSQLI_ASSOC);
        if(isset($row['user_email']) == $email){
            echo "email exists";
            // exit();   
        }
        if(isset($row['user_mobile']) == $mobile){
            echo "mobile exists";
            // exit();
        }
    }else{
        $stmt= $conn->prepare("INSERT INTO `users`(`user_name`, `user_email`, `user_mobile`, `user_password`) values (?, ?, ?, ?)");
        $stmt->bind_param("ssss",$name,$email,$mobile,$hashed_password);
        $stmt->execute();
        echo "successfull";
        $stmt->close(); 
    } 
}
 $conn->close();
?>