SQL Server 2012 :: Stored Procedure To Update And Insert In Single SP

I have Table Staffsubjects

with columns and Values

Guid AcademyId StaffId ClassId SegmentId SubjectId Status

1 500 101 007 101 555 1
2 500 101 007 101 201 0
3 500 22 008 105 555 1

I need to do 3 scenarios in this table.

1.First i need to update the row if the status column is 0 to 1
2.Need to insert the row IF SegmentId=@SegmentId and SubjectId<>@SubjectId and StaffId=@StaffId
3.Need to insert the row IF StaffId<>@StaffId And ClassId=@ClassId and SegmentId<>@SegmentId and SubjectId<>@SubjectId

I have wrote the stored procedure to do this. But the problem is If do the update. It is reflecting in the database by changing 0 to 1. But it shows error like cannot insert the duplicate

Here is the stored Procedure what i have wrote

ALTER PROCEDURE [dbo].[InsertAssignTeacherToSubjects]

@AcademyId uniqueidentifier,
@StaffId uniqueidentifier,
@ClassId uniqueidentifier,
@SegmentId uniqueidentifier,
@SubjectId uniqueidentifier

[Code] ....