To be honest i didn't use the NowTV search engine on either my NowTV box or Android phone.
Where you are absolutely right that Chernobyl is not found in the NowTV search section of the two above devices that i tried.
It shows up fine in my iPad Search.
But you have to get the title right, or you will find it is non-billed
Sounds like that you are using a Youview Box with your TV, which doesn't currently support the NowTV Entertainment Pass on the NowTV App.
Have a read of this help article on ways to watch NowTV.