Good site to check player details:
https://www.transfermarkt.co.uk/eliaquim-mangala/profil/spieler/90681
He got another contract year in March 2019, now til June 2020.
We don't know exactly why. Looks stupid if he won't leave now.
City don't have a squad space for him. He will never play a competitive match for City again.
Earning big wages without even playing a minute for the club always has a bad taste.
But he HAS a contract here, we have to accept if he wants to stay without any chance of playing football.
That's part of the business.
His career, his decision. If he doesn't like working in Turkey or elsewhere I could even understand.