By "vibration" do you mean the notification vibration that can be set for incoming calls or texts, etc? Or do you mean the haptic feedback vibration that you can feel when you tab the keyboard for composing texts, etc?
They are two different things, so be sure to carefully check your menus for them both.
If your notification vibration used to work, but has stopped, and it is set correctly in the menu, make sure you didn't change the default or the individual settings in the phone or messaging apps. The app menus over ride the default settings in the main menu.