The current version of Aperture at the App Store is 3.5.1 and requries OS X v10.9 or later. Version 3.4.5 won't run on Mavericks.
Veriify your payment method.
From the App Store menu bar click Store > View My Account then click Edit to the right of Payment Type
iTunes Store: Accepted forms of payment (Same for Mac App Store)
If you have 3.5.1 but it is not showing up in your Purchases list you really need to contact Apple what you are seeing is not right and will only cause problems down the road.