Riot Girl Tristana/Dreadknight Garen/Unchained Allistar unlocking issues

I just recently started playing the game again---I took a break for a year or 2---- and I have been trying to get the free tristana, garen, and Allistar skins, and I did everything I was prompted to do, such as follow them (League) on twitter, like them on Facebook, and subscribe to them on youtube, but nothing is working for me. Is there any way I can still get the skins? I started playing years and years ago, I just never got around to actually unlocking those free skins, which I deeply regret now.