Compare two numbers to in column and find which digits are missing

Hi Experts,
I have two sets of columns consisting of 7 digits numbers.
Both columns are suppose to be have same numbers ; Row B has full 7 digits. Column A has numbers less than 7 digit or some are missing when compared to Column B

Task to me is to find the missing numbers in Column A . For 1st row, it is 1&7 are missing, 2nd Row No 1 is missing.

Any guidance given for function is welcome!


eg
A B C
Missing N0.
33399 1333799 17
333555 1333555 1
557777 1557777 1
335577 3355779 9
77999 3577999 35
337799 3357799 5
7777 3577779 359

UDF

Function comp2numbers(n2 As Range, n1 As Range) As String

missing = ""
For i = 1 To 7
    m = Mid(n1, i, 1)
    If InStr(1, n2, m) = 0 Then
        missing = missing & m
        GoTo nexti
    Else
        ls1 = Len(n1) - Len(Replace(n1, m, ""))
        ls2 = Len(n2) - Len(Replace(n2, m, ""))
        If ls1 <> ls2 And InStr(1, missing, m) = 0 Then missing = missing & Mid(n1, i, 1)
    End If
nexti:
Next i

comp2numbers = missing

End Function

=comp2numbers($A2,$B2)

Checks for missing numbers and whether numbers of digits present are same e.g

33399 1333799 17
3399 1333799 137 only 2 3s

Hi Tony & John,
Thanks for looking in to my issue and resolving complex issue
Thanks
Karnik