If a case has been discharged/closed and you are receiving notifications for tasks that are due after the closing date, this is due to certain settings not being configured on those activities or reports.
To prevent repeating due dates for closed cases, go to the Configurator and open the specific activity or report and make sure the following boxes are checked:
Once these changes are made, a system administrator will need to go and delete any of the activities/reports that appeared after the close date. A report of Overdue tasks can be found under Case Tasks>DueSoon/Past Due
To identify which Activities and Reports have these boxes checked, navigate to Case Activities or Case Reports (Under Program). In the column marked Options search for the words PROMPTDELETE. This will indicate the boxes have been checked. You can compare this against the Column marked Repeat to see Activities and Reports with repeating due dates.