In the latest development update, there’s a way to report the purchase if you previously bought the game. You’ll need to provide the information you used for the purchase. You can find this information in your library when you open the game. (I just did this myself.)
Hey Smeatle!
We have a dedicated form you fill out on this page here:
https://zanithone.itch.io/a-house-in-the-rift/devlog/1489380/ahitr-itch-premium-...