PHP Fatal error: Call to undefined method mysqli_stmt::get_result() cant find fix

Question

Hi i'm making a login system for a online server and when i try to login i keep geting this error being thrown and i cant seem to find a way to fix this any help would be grateful. i have had a look and people say that its because of mysqlnd not being enabled but i have checked the database php version it is php 7.0 and it is enabled and i cant seem to find a fix, any help with this or tips on secure login would be grateful thanks.

This is my funtcion.php page which connects to process.php

   public function getUserByEmailAndPassword($email, $password) {

    $stmt = $this->conn->prepare("SELECT * FROM users WHERE email = ?");

    $stmt->bind_param("s", $email);

    if ($stmt->execute()) {
        $user = $stmt->get_result()->fetch_assoc(); // this line causes the error
        $stmt->close();

        // verifying user password
        $salt = $user['salt'];
        $encrypted_password = $user['encrypted_password'];
        $hash = $this->checkhashSSHA($salt, $password);
        // check for password equality
        if ($encrypted_password == $hash) {
            // user authentication details are correct
            return $user;
        }
    } else {
        return NULL;
    }

and then my forms process.php page

session_start();

require_once 'include/functions.php';
$db = new Functions();

// json response array

if (isset($_POST['email']) && isset($_POST['password'])) {

// receiving the post params
$email = $_POST['email'];
$password = $_POST['password'];

// get the user by email and password
$user = $db->getUserByEmailAndPassword($email, $password);

if ($user != false) {
    //user is found 
    $_SESSION['loggedin'] = true;
    $_SESSION["userid"] = trim($user["id"]);
    $_SESSION["first_name"] = $user["first_name"];
    $_SESSION["last_name"] = $user["last_name"];
    $_SESSION["email"] = $user["email"];
    //start session() and redirect to homepage.
    header("Location: ../dashboard.php");
} else {
    // user is not found with the credentials
    $_SESSION['Error'] = "Email or Password is Incorrect. Please try again!";
    header("Location:../signin.php");
}
}