Can't add Windows & Xbox (Apps and games) program to existing Partner Center publisher; Store sign-up creates a new account

We have an existing, verified Partner Center account (publisher "CMiC Global", enrolled in Commercial Marketplace and the AI Cloud Partner Program) and need to publish a Windows desktop app (MSIX) to the Microsoft Store under that same publisher.

• Account settings > Identifiers > Publisher > Add program only offers Microsoft 365 and Copilot. Windows isn't listed.
• Account settings > Programs > Other programs > Windows > Get started redirects to storedeveloper.microsoft.com, which starts a brand-new company sign-up. After D-U-N-S verification, our publisher name "CMiC Global" returns "Publisher name is not available" because our existing account already holds it.

Question: What is the supported way to add the Windows & Xbox program to an existing publisher without creating a separate developer account?

Support cases 2610200040009261 (Partner Center, opened Oct 20) and 2610260040007082 (Dev Center, opened Oct 26) haven't had a response yet. This is blocking a product release. Any guidance, or help routing the cases to the Store onboarding team, would be appreciated.