Pages app won’t open

I tried to open the pages app and it comes up and says ‘Unable To Install “Pages” you must purchase this app to install it’ I have used this app for aslong as Iv had the iPad so don’t understand what’s happening..

when i go to the App Store and click on the pages app it just sits on as if it is downloading but it is not.

any ideas??

p.s I have turned it on and off