One of the reward icons this year is a repeat...
That is to say, they're reusing the Slay Belle Kat looking icon as a reward again, and if I'm right that means you already unlocked this last year and just need to scroll down some in the summoner icon interface to see it.
I've seen a lot of misunderstood complaints about it not unlocking, and I don't know if this will be possible going forward, but if limited edition summoner icons ever get re-issued like this in the future, Riot should consider "popping" the icon up in the display order to sit alongside the newer icons, where people will notice immediately that they have it.