My skin disapear .... HELP

Hi my friend bought me a skin a few weeks ago maybe a month ago.. The steel legion lux I loved it ! I played with it alot but after I bought new champs so I stop playing for like maybe 1 week or 2 .. Yesterday I went in TB to play with her and when I check if I put my skin on its written '' Unlock'' .. so I dont have it anymore ???? how come ??

I really loved that skin, my friend spent money on this and I dont find it funny I would like to have it back ..

I dont understant why I dont have it anymore Please help