I seriously doubt they're going to give us the full series, and they don't 'owe' it to us either.
I certainly hope for you that in your country of residence advertising one product, yet selling another is also illegal.
The -only- link to the product advertised directs to the entry for the product on Greenlight. Their sales offer includes
a generic text about the series and the box image of the 3rd entry in the series (as does the series GL page).
Nowhere does the offer relate to a single entry of the five beyond the box art, which the Greenlight page by the
developer/publisher contains as well for the entire series.
Some shops may still try to argue that an offer of this kind falls into the 'too-good-to-be-true' category, but as this
does not really exist in online game sales that would be a losing argument. The last to try that was Gamersgate and
they ended up having to give 1,000s of users a yearlong 20% discount on the entire catalogue to compensate. That
was AAA games for 20-30 USD, making this offer pale in comparison by far.
Whether or not it's feasible to (try to) force a company without any means of contact beyond a single e-mail address
and no mention of an actual legal entity anywhere is another matter.