Hide Columns Based on Combobox (Form) In Excel - vba

Question

I have everything setup with different options for forecasts. I have done this in the past at a different job and I can't figure out where I am going wrong.
Private Sub ComboBox1_Change()
If ComboBox1.Value = "2 Weeks" Then
Columns("J:L").Select
Selection.EntireColumn.Hidden = False
Columns("M:R").Select
Selection.EntireColumn.Hidden = True
End If
If ComboBox1.Value = "6 Weeks" Then
Columns("M:O").Select
Selection.EntireColumn.Hidden = False
Columns("J:L").Select
Selection.EntireColumn.Hidden = True
Columns("P:R").Select
Selection.EntireColumn.Hidden = True
End If
If ComboBox1.Value = "12 Weeks" Then
Columns("P:R").Select
Selection.EntireColumn.Hidden = False
Columns("J:O").Select
Selection.EntireColumn.Hidden = True
End If
End Sub

Answer 1

It seems like your code should work just fine. I rewrote it to be more concise and it worked perfectly (with an Active-X control).
Private Sub ComboBox1_Change()
Select Case ComboBox1.Value
Case "2 Weeks"
Columns("J:L").Hidden = False
Columns("M:R").Hidden = True
Case "6 Weeks"
Columns("J:L").Hidden = True
Columns("M:O").Hidden = False
Columns("P:R").Hidden = True
Case "12 Weeks"
Columns("J:O").Hidden = True
Columns("P:R").Hidden = False
End Select
End Sub

Answer 2

In the title I included it was a form control. – phentrus 8 mins ago
The reason why I was confused and asked you in the comments above whether you are using a form control or an ActiveX control is because your quesiton title says "Form" but the code is for ActiveX.
For Form Control, paste this code in a module.
Option Explicit
Sub DropDown1_Change()
Dim DDown As Shape
Set DDown = ActiveSheet.Shapes(Application.Caller)
Select Case DDown.ControlFormat.List(DDown.ControlFormat.ListIndex)
Case "2 Weeks"
Columns("J:L").Hidden = False
Columns("M:R").Hidden = True
Case "6 Weeks"
Columns("J:L").Hidden = True
Columns("M:O").Hidden = False
Columns("P:R").Hidden = True
Case "12 Weeks"
Columns("J:O").Hidden = True
Columns("P:R").Hidden = False
End Select
End Sub
Next right click your Form Combobox and assign the above macro to it :)