Looks like the site itself was recently added under the web filter Fortiguard category "Streaming Media and Download", though do not know what other domains/ports are used by the service itself. You may have better luck blocking it via web filter/fortiguard. Mind you, you should use FortiView and drill down to the individual sessions of a device that is streaming/using the service just to see what is blocked/allowed through. The site itself uses a wildcard security certificate, so if your fgt is not using deep packet inspection, try blocking it wildcard web filter (via "*.disneyplus.com").
