I heard I can get free Tristana if I do something in facebook.

I don't have facebook account. If I make one how do I "link" facebook account to my game account so I get the free champion?

you go to their facebook eu.leagueoflegends.com/facebook and press the button, free tristana with a skin
and ofc you need a facebook to do so

That seems to give only skin. No Champion itself.

I am not sure even about skin. How can I see if I have the skin? I definitely don't have champion.

Go to your profile, then click on "Champion" banner, then look for Tristana, if her thumb is grey you did something wrong and you don't have her, however it thumb is coloured, you got her and probably you got skin too. If you want to check if you got the skin, click on thumb and when that Tristana window opens click on "Skins" tab, look for Riot Girl Tristana and if on the bottom of the skin pic it says "Owned" you got skin.

It could be that it takes some time to update because server has terrible issues at the moment, try relogging or just wait and check it tomorrow, if it still isn't there, your best shot would be at support but it will take some time until they respond. I helped as much as I could

I tried following instructions in http://www.leagueoflegends.com/board...ad.php?t=80451 but that didn't work either. I tried with Chrome and with IE and tried relogging to client several times. Nothing helped. I guess I have to try email to support.

I got exactly the same problem: "The Riot Girl skin has already been redeemed on your account." Ive tried to do the thing again few times, but still not working.