If the creator of the league (ex league moderator) left the league when the league is set as private, then it's not possible for anyone to join that league.
@Parmiamone could you elaborate more...
Your league you mean to say?If its your league then you can do that from moderator tools.
If it is not your own created league then you can't do anything.
There are several reasons for it, but one of the most important ones is to 'force' users to set an e-mail ont he account, so they can get access to the account again in case they forget password!
@BensonBSC mate it will happen. Trust me. Im in Egypt and i have 100 van dijk,96 greenwood 92 pogba 94 sterling 92 mbaape etc. U need to buy weak players and sell them for full price again to make money. Then scout or buy ur desired player.