Receiving hundreds of e-mails from different e-mail accounts (= you can't block all of them because there is always a new one being created)

This person clearly has no intention of stopping. This is also a lesson in why you should never, ever, give personal information to someone you don't know.

Rather than trying to impossibly block the ever changing addresses, see if you can block them by content. Look through the emails. Are there any repeated phrases in them? If so, set up a rule to block them by the repeating body text.

If that doesn't work, or the text doesn't really have common phrases, then the best thing to do is what has been suggested by AlWeir and BobTheFisherman. Create a new email account and abandon the old one.

You create a new email address and then add it to the trusted contacts in your account. Only then can you select the new email address as the primary ID and remove the old one.

By doing this, you can change the ID (email address) without losing your account or its data.

My suggestion is create another email address. Where is up to you. Once you have created it, move the mail that you want from your old email address to the new one. Send a email out to your known contacts that you have changed your email. Leave the old one running for at least a month unless you have data cap and look at it on the server not on Mail. Once your satisfied that that everyone of you contacts have your new email address, delete the old email address.

Change your email address and do not share it with spammers, etc.

How do I set up a second iCloud account?

To add another Apple ID to iCloud on an iOS device, go to Settings > Passwords & Accounts > Add Account > iCloud. Enter the Apple ID and password for the additional account. On a Mac, go to System Preferences > Internet Accounts > Add Other Account > iCloud