You can uninstall Evercontact directly within your domain's Evercontact settings as you see in the bottom right here. One click, and you're done! Afterwards, please do leave us a bit of feedback on why you decided to leave. Thanks!
Alternatively, go to your google apps domain admin console & click on "apps".
Click on marketplace apps
Click on Evercontact
Click on the trash can icon in the top right.
And then click "remove app".