You can still use a Union Query. In reading your response, I am not sure if you understood what Helen was getting at. (If you did, I apologize). She was asking if there is a Primary Key involved that remains with the customer when they cancel that would be found in each table.
Even if there is not, you can Union the two together. You need to write Union Queries is SQL language (it is not that hard and the help files are excellent if you are not familiar with it). It would look like this:
SELECT [Name], [Address], [Balance] As [AmountStillOwed]
FROM [tblCancelledAmountStillOwed]
UNION SELECT [Name], [Address], "0" As [AmountStillOwed]
FROM [tblCancelledOweNothing]
The "AS" statement allows you to import a field from a table and rename it.
HTH