We cannot give refunds ourselves, but you can ask Apple for one.

When you purchase an app from the App Store, only Apple has access to the purchase information that is associated with your Apple ID. To protect your privacy, these details are not shared with developers. As a result, we cannot issue refunds ourselves.

If you are not happy with Things, you need to request a refund from Apple. Whether or not a refund will be given is entirely Apple’s decision.

You can find Apple’s guidelines on refunds here.