Hi disneygirl1977,
welcome to the Apple (user-to-user) Community!
Re: "iTunes purchase missing…"
Am no expert on iTunes, yet your request surely deserves some response!
Apple support's online article:
Manage your iTunes Store purchases and settings on iPhone - Apple Support
Eg: says:
"In the iTunes Store, tap More, then tap Purchased".
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Buy movies and TV shows from the Apple TV app - Apple Support
Eg says:
"To see all of the movies and TV shows that you purchased, choose Movies or TV shows from the pop-up menu, then click Library in the navigation bar".
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If needed: See how to: Redownload TV shows and movies that you purchased - Apple Support
or
How to: Download and stream shows, movies, and events from Apple TV+, MLS Season Pass, and Apple TV channels - Apple Support
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Re: Where has my purchase gone?
if you haven't found it, and need an explanation:
You may need to reach out to iTunes Support (online chat / phone / email etc.)
There is a "Get support - start now " link at the bottom of their website (link below):
iTunes - Official Apple Support
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Re: "If it is no longer available, am I going to be reimbursed the money I paid for it?"
Refunds generally need to be requested, and then wait until a decision is made from Apple.
How to: Request a refund for apps or content that you bought from Apple - Apple Support
All the best :-)