So effectively they don't provide refunds at all? Non-withdrawable store credit should probably be illegal too.

V-bucks aren't really store credit though. They're non-refundable and it makes sense because you can also get them through in-game actions.

Maybe an 'Oops! I didn't mean to do that.' undo button immediately after buying some. But it would be better just to make the checkout process explicit like they do on PC.

I'm sure they can manage to track which fakebux you paid for and which ones they gifted you. The is zero consumer benefit to having intermediate currrencies that cannot be be changed back into real money. It's entirely a dark pattern used to make you spend more by obscuring costs and generating leftover amounts that you can't really use without inserting more cash.