How are you trying to set the memory limit? phpinfo() shows current PHP reserved memory limit, and this is what is available due to php.ini having that set as a memory limit.
Writing this to the Apache .htaccess file in your script directory might work if your server supports setting PHP commands through .htaccess:
php_value memory_limit 2048M
Since it may be possible that .htaccess commands for setting PHP values are turned off. Then you can also try this from PHP code:
ini_set('memory_limit', '2048M');
If this doesn’t work and .htaccess also doesn’t work, then you need to contact the server administrators.