Missing skins

For the past week I was away at work and could not log in/play league. So I get home moments ago, patch the client, and see there are some winter event skins out at the moment. I seen that Workshop Nunu was available for me to purchase, but I know for a fact Ive owned that specific skin for months now. It was mystery gifted to me. Can someone tell me why my skin was revoked from my account, and if I can somehow get it back without having to purchase it?

Im also positive that my account has never had any type of offenses that would cause Riot to ban me, or revoke any of my in-game purchases. The worst that has ever happened to me was my "Honorable opponent" loading border was taken away from me a long time ago.