Mac Pro won't let me sign out of Imessage.

Hi,

I have always been signed out of imessage on my MB pro since updating to el capitan from lion a month ago. I was able to log out during this time by going to preferences --> account and signing out.

Yesteryday I decided to log in imessage to try it out again. After playing with it for a few minutes, I decided that I don't really need to use this feature and tried to sign out. I couldn't do it. When I go preferences --> Accounts, I can see my Apple Id but there are no options to signout/enable etc. It shows a blank page to the right. Also I have been getting notifications from imessage even after turning off notifications from settings. I have restarted the computer and quit the application multiple times but I stay logged in and keep getting messages. Going to settings --> internet accounts --> icloud --> doesn't show imessage to check off/ Imessage (faded) can also be seen running on activity monitor even after quitting the app.If anyone knows a way to stop this, please let me know.

Thank you.