As far as I can see, "noch nie" means "never", but "nie" also means "never".
So when to use each form? Eg
Ich habe diesen Film nie gesehen
Ich habe diesen Film noch nie gesehen
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It's getting clear if you translate noch nie with not until now.
Your first sentence just states seen=yes or seen=no. You could use it in a neutral, informational situation or to express your disinterest.
The second sentence implies there's still an opportunity or will to try it. You could for instance use noch nicht when you're at the cinema and you discuss which movie to watch next.