Background:

I own copies of several fairly expensive paper books published by O'Reilly Media. One of my primary reasons for buying these books instead of alternatives from competing publishers, was that inside the book, the following offer is advertised:*

Get even more for your money

Join the O'Reilly Community, and register the O'Reilly books you own. It's free, and you'll get:

• $4.99 ebook upgrade offer
• 40% upgrade offer on O'Reilly print books
• Membership discounts on books and events
• Free lifetime updates to ebooks and videos
• Multiple ebook formats, DRM FREE
• Participation in the O'Reilly community
• Newsletters
• Account management
• 100% Satisfaction Guarantee

Signing up is easy:

1. Go to: oreilly.com/go/register
2. Create an O'Reilly login.
3. Provide your address.
4. Register your books.

Note: English-language books only

(An image of the same page, as it appeared in a different O'Reilly book from 2015, is shown below.)

This gave me to understand that by buying the books, I was also buying the right to redeem this offer.

I attempted, a few days ago, to take advantage of the "$4.99 ebook upgrade offer" for a couple of O'Reilly books of which I have paper copies. I have performed the steps above, except for the last one, because I could not find any option to register the books. Because of this difficulty, I contacted O'Reilly, who said, to my considerable surprise:

Thanks for reaching out. We've recently discontinued the "Register Print Books" feature on the website, as well as the "$4.99 Ebook upgrade" deal tied with it. This feature was disabled because we've shuttered our online store and are no longer offering the direct sale of ebooks or print books.

To me, this seems unacceptable, because:

• the offer has no expiry date; and
• O'Reilly appears to be a "going concern", so is presumably obliged to fulfil the written offers it has made to its customers; and
• books advertising the offer are still being widely sold in bookstores (new, not second-hand), so even today, customers could still be buying books on the basis of the offer.

My question:

Under English or US law, and given the above facts, is O'Reilly engaging in false advertising?

Update: Image of a page showing the offer:

* This wording is taken from an O'Reilly book published in 2015. Books from other years might have marginally different wording, but for all the books I have checked so far, the offer was essentially the same.