3 years ago I bought a game for $10, now the same game has a free older version and a $25 current version. This site even tells me I own the game since I purchased it but when I go to download the current version of the game it only gives me the older free version with no option for the current version which I paid for. How do I get the game that I'm told I already bought? 

It is this issue: https://itch.io/t/5069732/do-players-lose-access-to-paid-itchio-games-after-pric...

You did not buy the game. Or rather, you bought access to all files that are paid. There are no paid files, since the game is pay what you want with minimum price of 0. You also gained access to all bonus files of the $ 10 tier.

The developer chose to remove the $ 10 tier. Which is a bad usage of the feature. The whole feature is ill implemented and ill understood to begin with.

For that particular game, you did not buy the game as such, you gave money to support the developer and gained the perk of accessing the free version earlier. You did not buy access to the game as such. The game in question seems to be planned as a free game.

What the developer should have done is this: have 3 tiers. 0, 10, 25.

But then the other design flaw of that feature becomes visible: you can't increase your tier by paying the differnence.  This pricing feature needs a major overhaul. It creates a lot of bad user experiences.