Are you sure the uploaded files are supported by OnSign TV?
Files transferred through the FTP (File Transfer Protocol) are not filtered in the same way as when you drag them onto the OnSign TV website. If you have uploaded – through FTP – a file type not supported, OnSign TV won't list it on your Files tab, but it will affect your space usage. We recommend that you delete unsupported files on your FTP client.
You can see a list of supported file types at How can I upload files?.