Messenger app starts automatically many times when I don't want to start it. And there is also no exit button in this app.So it always try to run in background. How to prevent Facebook's Messenger apps from auto starting in background?
If you are a rooted user, use any firewall app (plenty of them are available at Play Store). Some of them I know of are Droidwall, AFWall+, etc.
Also, you can use Greenify to hibernate apps which are not in use.
I hope combination of any Firewall and Greenify will definitely solve your problem.