By adding intuitive confirmation steps, we’ve done everything we can to limit accidental purchases from the game. When purchasing with Diamonds, you will always be notified, and asked to proceed before spending any actual Diamonds. This has done very well in limiting such instances.
Because Head Ball 2 is a live, online multiplayer game, reversing changes would adversely affect other players you've interacted with. As we can’t turn back anyone's in-game progress, or remove features, providing this refund would put you in a privileged position, which we see as unfair to other players who earned the same item or upgrade through their Diamonds or gameplay.