@Gyoza I have had taht happen to me as well. Not on this site though, but on other sites.
I don't think is the fault of the casino, rather the affiliate that doesn't have that special offer anymore. Unfortunately this happens A LOT (not singling out any site or affiliate). Make sure to ask the affiliate you sign up through, if the bonus still applies.
Lastly contact whoever you signed up through and ask them help you out. Hope they can help you, but a piece of advice is to check that offer still exist with chat before using it.