If You want to block just contact form but You want to display contact page You can put in override\controllers\front\ContactController.php:
<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-html -->
<?php
class ContactController extends ContactControllerCore
{
public function postProcess()
{
if (Tools::isSubmit('submitMessage'))
{die('Form disabled');}
else
parent::postProcess();
//return null;
}
}
<!-- end snippet -->
This will disable ability to send mails.
Then You can cut contact form from theme: /themes/YOUR-THEME/contact-form.tpl
to not display contact form at all
**After this You have to delete file /cache/class_index.php to refresh classes in prestashop.**