Adding A Credit Note To A Statement Report?

I need to add a credit note to my statement report which minuses a wrong invoice. For example, if a wrong invoice is given to a customer, then the user uses a credit note form which updates in the credit note table and this shows in the statement report as a minus. I hope that's not too confusing. The problem comes when I need to add it to my report. It will have the same date as the original invoice and the same price, it will just be shown as a minus.

My statement starts as a form which the user has to enter a start date and an end date and select a customer from a combo box, they then click generate statement which opens the report. How would I add the credit note in? I want it to be in the same date selected but the query for the report only contains the invoice date and not the credit note date. If I add this into the query, it clashes and brings up a blank report. Is there anyway to do this? Will I need to create another query for the credit note and add it in as a subreport? Will I have to add another startdate and enddate for it too as a subform in the statement form?