How can we have "403 Permission Denied" for our folders?

Hello,
We run a multisite/subfolders site on the root directory. We do have the very basic configuration to our .htaccess file. Nothing complicated.
When someone types on the browser address
“http://multisite.com/wp-content/blogs.dir/43/files”
they can see ALL files under/in that directory. The same happens if they type eg:
“http://multisite.com/wp-content/plugins/contents-of-the-box/languages/”
We do NOT want that.
We would like to block public directories access for all folders.

We tried putting:

#BEGIN Deny Directory access
Options All -Indexes
#END Deny Directory access

in the .htaccess file but it was denied by the host system. Are you aware of some other way of achiving the above?

Thank you for the help,
marikamitsos