Elseif function not returning correct answer

A Worksheet BeforeDoubleClick: Run Procedures by Double-Clicking Cells

• Compare the cells' addresses as mentioned by FunThomas in your comments.
• Use the Select Case statement as suggested by Tim Williams in your comments.
• Set Cancel to True when the cell is a desired one so you don't enter the edit mode of the formula bar.
  Leave it as is or set it to False when not.

Sub WorksheetBeforeDoubleClick(ByVal Target As Range, Cancel As Boolean)
    Cancel = True ' disable entering formula bar via double-click
    Select Case Target.Address(0, 0)
        Case "F6"
            MainFacture
        Case "F9"
            MainProforma
        Case "F12"
            MainBL
        Case Else
            Cancel = False ' enable entering formula bar via double-click
    End Select
End Sub

Sub MainBL()
    MsgBox "BL"
End Sub
Sub MainFacture()
    MsgBox "Facture"
End Sub
Sub Main_Proforma()
    MsgBox "Proforma"
End Sub

Two different cells may have the same Value, but different address. The Range.Address property comes in handy.