Movie with girl locked in a basement

Hi.I have been wanting to no this film or short film that I watched on free view. About ten years ago. It's wen a girl gets knocked down by a van then they sort of kidnap her and lock her in the basement. There is a boy down there too. But at a certain time he changes into a monster and feeds on humans. Long story short he's cursed I think. And at the end he reversed it to his parents. Help me lol

That sounds an awful lot like the Masters of Horror episode "Fair Haired Child".

Thank you. That is the one