How about if you put that notice on the website, but also write it out explicitly and post it via registered mail to the Meta lawyers. Explicitly state that the content on your site is not licenced to be scraped for free and any usage must be paid for (eg $10/GET with penalties for non-payment), and that any usage of the site by Meta or their agents is an indication that they accept the terms fully.

Then check your logs and start sending appropriate invoices.

Then after 1yr of unpaid invoices: <profit>

I imagine the general problem is still that you're trying to bind a party without a live human who is plausibly authorized to bind them making a reasonably active decision to do so. IANAL, but AIUI "doing XYZ normal thing means you accept my contract" is already on shaky grounds, whereas never actually having the other party affirmatively agree (esp to a contract of adhesion) makes it super unlikely any non-kangaroo court would do anything besides throw your case out.