w3 disc enhanced setting showing old post for non-logged in users

Hello there,
Yesterday something gone wrong at my site and it didn’t let me or registered member logged in and we were getting 500 error.

so i asked my server guy to fix. He did same when i asked what he did he replied Regarding the 500 error, they have changed the permissions for the files to 644 and folders to 755, changed ownership for all the files to admin user. Changed the PHP from suphp to mos_php (php-cgi).

Today some user who doesn’t use login complaint that he can’t view lates post I checked in different browser and found content was showing before that error came yesterday. I changed w3 total cache page cache setting to basic then problem solved but still i set advanced cache my site showing old content.

Please tell how can i fix it