Are you capable of linking directly to the file, and just HTTP indexing that is not working? What is the HTTP error you are receiving when you try?
Honestly, if you are in direct contact with the site administrator, they should be able to give you clear answers as to what is present on your space, and how to successfully access it.
If your site admin is unable to access these files, then it is unlikely we will be able to either.
Folders with the CHMOD 755 will typically HTTP Index under most default webserver settings, otherwise you may need to place a .htaccess file containing the following lines, into that folder.
Options +Indexes
IndexOptions +FancyIndexing
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