Share your experience!
Let me understand this
1) you had whastapp
2) your free trial expired
3) uninstalled the app
4) try to redownload the app?
Which country do you live in? are pay apps available in your country? (not just whatsapp but pay apps in general) if not then that most likely the reason, you can not longer use the free version of whatsapp and since you can't pay for it you can't install it
How about on the play store app (Not the website) can you see whatsapp?
try this
settings > apps > all> play store > clear everything > restart your phone
Anytime, Don't forget to give Kudos