SMB, WebDAV, DLNA have a whole different set of configuration files to fight with.
If you can echo $date > /[insert Mount Point Of The Usb Drive Here]/myusbwritetest.txt && cat /[insert Mount Point Of The Usb Drive Here]/myusbwritetest.txt you know you’re able to read, write as the root (eg: Administrator in Windows parlance). rm /[insert Mount Point Of The Usb Drive Here]/myusbwritetest.txt removes (deletes) that test file.
df -h will show you what is the specific mount point/storage device target path.