I'm sure like with most events they release these types of stuff in batches. I remember when they gave the mystery skin for good player and I didn't receive mine till about a week after they were giving them out. You have to remember there are millions of accounts they need to give it too. I'd say give it a week and if you still haven't gotten it contact support and they'll help you. Also remember that I believe with the icon and the mystery champion/skin. It's only going to people who not only participated but also are in good terms eg: not ban from the game before (not sure about chat restriction)
All in all just give it a few more days and if you still haven't gotten it contact support!