I guess it is someone pretending to be them possibly as well as they wrote other songs than this on the album but those are still active. Sadly YouTube doesn't verify ID before someone can make a copyright claim pretending to be someone else.
If they're not the real writers, YT wouldn't take it down. You have to provide real proof. Even if they are not the real writers, Starship could've solved this after a couple of hours, because they're a big company, not a vlogger.
The weird thing about this is they only did this on YT.