Most properly done auth for sites that protect your account will not respond in the affirmative or negative if an account with a specific username/email exists. You'd also have to have it log in to delete your account, which means scripting to navigate every single site. It's just not a thing.

The security implications of what you're asking for are terrible. Imagine I get an email passwords combo, I use a service to scrape the web of everywhere else that email exists, now I only have test a handful of sites not all of them.

Keep changing all the passwords you can. If you've forgotten the site, then as long you change the important ones - worst case they get an already public email and password that's not repeated anywhere important.

As for payment info, if you get a brand new card number that's the easiest route. Otherwise you'll have to rely on the expiration and new security code to eventually invalidate anywhere the number remains.

Using any kind of proxy card, like privacy.com is a good idea. Failing that, at a minimum have a separate savings account and only keep whatever you need available on the debit card to minimize potential losses. Additionally, it's recommended to use a credit card as they tend to offer better fraud protection then a typical bank card (citation needed).

Note, I am not a financial or security expert. Just some bloke sharing what works for me.

Mine?