Unfortunately Stake still has not made any contact with me regarding my complaint. They also failed to respond twice to the third party complaint service who tried their best to get in contact with Stake, sadly without any success.
I don't feel like they have to contact you. It's not like they're making you go back to gambling, you have a lot of tools available. You can for example block them in your mailbox or in an extreme situation stop using it. There's plenty of email providers out there. IMO they should give you a way to unsubscribe, but if they did not, it's not like you have to cry in the corner or give up and start gambling again. Don't let some automated mailing system get the better of you. You're not a child anymore, things like that happen every day!