New Company set up but invoices paid to an old account

Hi,

My company accounting file was migrated to MYOB Essentials last November.

Invoices for one customer - that were paid and closed in the previous accounting software - re-opened after migration to MYOB Essentials. 

I raised a credit note for the customer - but have no invoices to apply the credit note to, nor can return the funds to the customer as this would raise a bank transaction that I would need to reconcile.

Any advice on how to do this without affecting the GST is appreciated.

Tabatha