Highlighting/Deleting Special Charahters In A Range

I have a column that needs to be text format, but it needs to include only digits (0-9), no letters, no special characters. Also all cells need to have 7 digits.

I am trying to do a couple of things:
1 : Hightlight the cells that contain Strings with Non-Digits characters
2 : Highlight the cells with less than 7 characters (I have the code, it is below)

I have tried many ways to get #1 but I am stuck.

Help please.

This highlights the cells with less than 7 characters:

Sub StringLength3() ' IT WORKS!

Dim strTest As String
Dim i As Integer
Dim Cell As Range

'Select Range
Worksheets("tres").Activate
Worksheets("tres").Range("A2", Range("a65536").End(xlUp)).Name = "RangeA"
Range("RangeA").Select

For Each Rangea In Selection
i = Len(Rangea)
If i 7 Then
Rangea.Cells.Interior.ColorIndex = 7
End If

Next Rangea

End Sub