That's odd. We suggest getting in touch with our YouTube Premium and purchases support team. Here's how: https://goo.gl/akUj5G . Hope this gets resolved.
@TeamYouTube I purchased a movie from Youtube amd it WILL NOT let me play it or cast it. Won't work for smartphone or smart TV in either the YouTube app or the Google Play Movies and TV. Either refund me or help me please! Second week spent trying to figure this out 
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