Why do I receive an invoice (outstanding amount) even though I already paid?

See below for the reasons as to why you did receive the invoice:

• In case you received a down payment invoice, you will, after the goods have been shipped, receive an invoice for the outstanding amount. 
• In case nothing has been changed to the order, the open balance will amount to 0.00 euro; in which case you can add this invoice to your down payment invoice.  
• In case there were changes to the order between the moment of the down payment invoice and the open balance invoice, you will either receive a credit note or an additional invoice amounting to the difference in value.