Q: why do i have to pay for pages, numbers and keynote again?

If you purchased the physical installer disk, then use that disk again and after installing, open the App Store to update and claim them. When you do this you should not have to pay for them again to download them.

If you purchased it on the App Store and are sure you are using the correct Apple ID, read this article to make sure you haven't hidden them:

Hide and unhide purchases in the Mac App Store - Apple Support