I CANNOT LEAVE THE LEAGUE.

Remove your UID. Also, no need to post in CAPS.

As far as your issue goes, have you created the league and given the ownership to someone, or does the game assume that you are an owner for some reason?

Bro I am not the owner. The owner has first made me admin and then made me the owner. But somehow our grow had two owners and the second owner gave his ownership to somebody else.Hence my owner ship is gone but fc mobile is telling owner of the league cannot leave you should delete but I don't have the option to delete or remove others

So, you were granted ownership at some point, and it looks like the game believes that you still are the owner.
There are a few ways to deal with it, 2 will require your own input
- Have a chat with the current owner and see if they can boot you out of the league. If not, then ask what error code the owner is getting. 
- Alternatively, you can ask to be made an owner temporarily, leave it for 24+ hours, then give it back, this may resync your and the league status. 
- If the two options above do not work or you are not on good terms with the owner, you will need to raise a ticket with Helpdesk via the in-game menu.