Transact SQL :: 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] .....