This is how I would have done it.
Make the new account (with a throw away email) , take the 1000$ bonus, withdraw it (if possible). Change the password to something you definitely won't remember and log out. Also delete the throw away email.
Repeat this with you other account.
That way you can't log in anymore and also can't recover the account since you don't have the email. Easy solution for this.
And with the 1000$, get some help for your addiction. I know I make it sound easier than it is but for the self exclusion that's a great way to get rid of your account there.
That's a good idea, and gambling addicts should do things like that when they decide to stop gambling at a platform, if the casino allows to change the email address of the account though. But what throw away email provider allowing to delete mail box easily do you recommend?
The most famous disposable email provider Yopmail deletes emails but not the email addresses for example, so you will be always able to use it again to get back your account access.