That's frustrating, clearly advertised but not working. First, try clearing the Omen Gaming Hub cache or reinstalling it. Also check if your Xbox account region matches the promotion's eligibility. If it still freezes, contact HP support directly; they sometimes need to manually trigger the offer on their end.
On a side note, if you're into sports titles, check out this game, it's a volleyball sim with surprisingly deep strategy and smooth mechanics. Not related to your subscription issue, but worth a look for downtime.