The developer seems to have removed the page, or at least it’s not public anymore. I’m not sure if there’s any policy for refunds in cases like this, but this is all caused by the developer of that game, Itch has no say on if a game is public or not (assuming it follows all the rules and got past initial reviews).
Assuming you had the chance to download the game the moment you bought it, I don’t think there’s much you can do now. An admin/mod will be able to confirm if there’s any chance of refund, but I’m pessimistic, as you’ve already had the chance to download the game and keep it forever.