there are three ways to solve this issue, you can ignore the promotional email, you can unsubscribe, or you can log in and change the email to the one that you rarely use, we all have disposable emails, it only proves that you are still not cured and a mere mention of gambling site will get you irritated, a person that is cured of gambling will not get agitated or irritated from this issue, based on your post you still hate Stake.com for the many loss you incurred.
Recovering from addiction is a very difficult process. In this case, Stake.com knew perfectly well that the situation was very difficult since the user himself asked to close the account. In my opinion, Stake.com knew that a user is addicted to gambling and continued to send him promotional offers, it was very inappropriate. In my opinion, such a person should be helped, not made difficult in this way.
on the other hand you also have to know that stakes are business people and we can't make anything or order anything, promotion is something that is natural and not excessive either.
the most important thing is how the person who gets the email (in this case the OP) reacts to it.
addiction is the personal fault of the gambler as for the gambling house I don't think it has anything to do with it because they are businessmen and their source of income there