Maybe you're editing the wrong php.ini.
If your domain runs as Apache module, then sure, you're editing the correct file ("/etc/php5/apache2/php.ini").
If your domain runs as FastCGI application, then you have to edit "/etc/php5/cgi/php.ini".
You can check that by clicking on your domain name (when you're on tab "Websites & Domain in your control panel), and there under "Web Scripting and Statistics" is "PHP support" (also make sure that drupal support is checked if you're doing something with that).
Or create new ".php" file, something like "test.php" and type there:
<?php phpinfo(); ?>
Save the file and check it in your browser, and you can check there also for "Configuration File (php.ini) Path".