I've had similar experiences several times with emails directly from casinos stating I have a special bonus or free money waiting in my account, login and nothing there. I usually just leave it be, I did'nt ask in the first place.
Casinos do need to get it right when they're going to send out these type emails to their players, it just don't look good and seems their trying to get an extra deposit using false pretenses.
In your case it sounds like you won the bonus, so good to hear you got it.