Hello
Can you verify that the settings is written to your .htaccess or php.ini file?
Open you .htaccess file and look for the following section:
# BEGIN CUSTOM PHP SETTINGS
php_value post_max_size 256M
php_value max_input_vars 5000
php_value upload_max_filesize 128M
php_value max_execution_time 300
# END CUSTOM PHP SETTINGS
I am also interested in what hosting provider you are using? It might be an issue with that they don’t allow you to change any settings.
Are your permalinks working as they should? If not then this might be an issue with the webserver configuration, for instance if using apache then you must configure the server to allow override through the use of .htaccess files.