Access denied from subfolder to root sub folder

I have my site structure as follows:

mysite.co.uk/admin/file.php

my images are stored:

mysite.co.uk/files/images/product/

The problem I am facing is the the code on the

mysite.co.uk/admin/file.php will not let me read the images in the products folder:

My code is as follows:

 $dir = "../files/images/product/";
    $dh  = opendir($dir);
    while (false !== ($filename = readdir($dh))) {
        $files[] = $filename;
        }
    sort($files);
    foreach ($files as $filename){
  echo "<option value='". $filename . "'>" . $filename . "</option>"; 
   }

Please any advise is welcome

I can see the files stored in ../files/images/ when changing the $dir to ../files/images/product the server send a HTTP502 error, which seems a bad gateway.

I have tried to allow url files/images/product in the firewall however that doesnt work either.

I have also tried to change the permission on the actual folder 0755 to 0644 but that caused a lot more problems

The server is godaddy.

Please any advise is welcome