同じ状況になったので、Microsoftに英語でサポートをお願いしました。それなりにやりとりして、コードを送ってもらえることになりました。

Thank you for contacting Microsoft Surface Support.

Today, you contacted us because you needed to have your Surface Duo unlock code.

We are glad that we addressed the network scenario by starting an internal consultation so we can have the code created. Please wait the code within the next 3-5 business days.

In case you need more assistance, do not hesitate to contact us.