Why can't I download/watch the movie I rented ?

So I decided to rent a Harry Potter movie, it was downloading fine until I clicked on it and it said my phone didn't have any memory. So I deleted a couple apps and made sure I had sufficient memory. I went back to download it but it wasn't there, and when I go to rent it says I have to rent it again. The movie never finished downloading... Anyway, I found the movie in my Videos app, but the play button isn't pure black its kind of shaggy gray ( aka you can't click this ). So now I can't play or download the movie but it's in my videos app ? How do I fix this. If it helps the movie is 5.78 GB while I have 6.40 GB available. And I'm trying to watch it on my iPhone 5s, it is up to day.