In app/code/core/Mage/Customer/Helper/Data.php this is hardcoded const VAT_VALIDATION_WSDL_URL = 'http://ec.europa.eu/taxation_customs/vies/services/checkVatService?wsdl'; whilst new url is (I think) const VAT_VALIDATION_WSDL_URL = 'http://ec.europa.eu/taxation_customs/vies/checkVatTestService.wsdl'; Explained here https://ec.europa.eu/taxation_customs/vies/technicalInformation.html Needs check from Dutch DEV