Steven Zahm@ Nana
AJAX is not a product … it is a web technology. Basically it allows a web page to tale to the server without have to reload the page. In WordPress ../wp-admin/admin-ajax.php is used to “talk” to WordPress. This is a core WordPress file. If access to the file was blocked, it is likely breaking other things in WordPress too which may not be as obvious.
It is unfortunate that the web host choose not to assist because they can fairly easily tell if it is a server configuration issue blocking access. So that makes resolving this a bit more difficult than it needs to be.
The first step to diagnose this is to do both the conflict checks because it is possible that a theme or plugin is causing this caching and security plugins.
If following these do not help, then it could be block applied in the server’s .htaccess file.
Let me know what you learn by doing the conflict checks. If they do not resolve it, I’ll need both and WordPress admin login and an FTP login. The details can be posted here as a private reply.