I didn't know this, Yahoo apparently is taking care of the advertisements on Bing?!

On the Dutch version of Microsoft Advertising,

"# Wilt u meer weten over de advertentiemogelijkheden voor Bing? Dan kan het Bing Sales team u er meer over vertellen. U kunt ze bereiken op het internationale telefoonnummer 0800 0250118 of per e-mail op nl-klantenservice-ysmcc.yahoo-inc.com."

Translated:
"# To find out more about advertising opportunities for Bing? Then the Bing Sales team tell you more about it. You can achieve on the international telephone number 0800 0250118 or by e-mail nl-customer-service-ysmcc.yahoo- inc.com."

Maybe because Microsoft adCenter is limited to a small number of countries: US, UK, Canada, France, Singapore.

https://adcenter.microsoft.com/customer/SignupPreview.aspx?adv_market=en-us&s_int=118