I believe your issue has come about because if a player decides they don't want the promo and unsubscribe to it, although all funds in the real balance will remain, any funds in the bonus balance is forfeited. In the conditions we did put "Unsubscribing from this promo after placing any bet will result in funds in your BONUS balance being forfeited." I did apologise in a previous post as these conditions may not be obvious enough so we definitely need to work harder to make them more prominent so players don't feel they have had their money taken in any way and I apologise to you again if it seems like that's what has happened.
After this incident, I think you should find a way to make sure that users've read the promo terms and fully understand them. You can for example display the terms on a pop-up window and don't allow the user to subscribe to the promo until he clicks on an
agree button.
Forfeiting the bonus balance when a user decides to unsubscribe from a promo doesn't make much sense, imo. It works totally in favour of the casino and it would become more fair if you start deducting bets from the bonus balance then the real balance.