In Settings, Notifications, Calendar - it is set as Allow Notifications. And further in Upcoming Events, Invitations, Invitee Responses, Shared Calendar Changes, Events found in Mail it is set as Show in Notification Centre, Sounds on, Badge App Icon, Show on Lock Screen & selected alert style as Banners. Please let me know it should be banners or Alerts. Earlier I set it as alerts but still it was not alerting. Please help.