For the records and future maintenance, here are the urls where we got the wsdl files:

PRODUCTION:

ad_insight:          https://adinsight.api.bingads.microsoft.com/Api/Advertiser/AdInsight/v13/AdInsightService.svc?singleWsdl
bulk:                https://bulk.api.bingads.microsoft.com/Api/Advertiser/CampaignManagement/v13/BulkService.svc?singleWsdl
campaign_management: https://campaign.api.bingads.microsoft.com/Api/Advertiser/CampaignManagement/v13/CampaignManagementService.svc?singleWsdl
customer_billing:    https://clientcenter.api.bingads.microsoft.com/Api/Billing/v13/CustomerBillingService.svc?singleWsdl
customer_management: https://clientcenter.api.bingads.microsoft.com/Api/CustomerManagement/v13/CustomerManagementService.svc?singleWsdl
reporting:           https://reporting.api.bingads.microsoft.com/Api/Advertiser/Reporting/v13/ReportingService.svc?singleWsdl

SANDBOX:

ad_insight:          https://adinsight.api.sandbox.bingads.microsoft.com/Api/Advertiser/AdInsight/v13/AdInsightService.svc?singleWsdl
bulk:                https://bulk.api.sandbox.bingads.microsoft.com/Api/Advertiser/CampaignManagement/v13/BulkService.svc?singleWsdl
campaign_management: https://campaign.api.sandbox.bingads.microsoft.com/Api/Advertiser/CampaignManagement/v13/CampaignManagementService.svc?singleWsdl
customer_billing:    https://clientcenter.api.sandbox.bingads.microsoft.com/Api/Billing/v13/CustomerBillingService.svc?singleWsdl
customer_management: https://clientcenter.api.sandbox.bingads.microsoft.com/Api/CustomerManagement/v13/CustomerManagementService.svc?singleWsdl
reporting:           https://reporting.api.sandbox.bingads.microsoft.com/Api/Advertiser/Reporting/v13/ReportingService.svc?singleWsdl

TEST:

ad_insight:          https://adinsight.api.bingads.microsoft.com/Api/Advertiser/AdInsight/v13/AdInsightService.svc?singleWsdl
bulk:                https://bulk.api.bingads.microsoft.com/Api/Advertiser/CampaignManagement/v13/BulkService.svc?singleWsdl
campaign_management: https://campaign.api.bingads.microsoft.com/Api/Advertiser/CampaignManagement/v13/CampaignManagementService.svc?singleWsdl
customer_billing:    https://clientcenter.api.bingads.microsoft.com/Api/Billing/v13/CustomerBillingService.svc?singleWsdl
customer_management: https://clientcenter.api.bingads.microsoft.com/Api/CustomerManagement/v13/CustomerManagementService.svc?singleWsdl
reporting:           https://reporting.api.bingads.microsoft.com/Api/Advertiser/Reporting/v13/ReportingService.svc?singleWsdl