This issue is almost certainly tied to your "Windows and Windows and Phone Annual Developer Registration" subscription. The system links the developer account's verification address directly to your Microsoft Account, and it often locks that specific address field to maintain billing and identity integrity for the subscription.
The key to resolving this is to manage the address through the dedicated Visual Studio Subscriptions (formerly MSDN) portal, not the general Microsoft account settings. Please log in to the Visual Studio Subscriptions portal using your Microsoft account. Once logged in, navigate to your "Subscriptions" and then to the "My Account" or "Contact Information" section—this is where the source of this locked address resides.
Updating your details there should propagate the change back to your core Microsoft Account profile and resolve the conflict. I am confident this targeted approach will solve the problem that the general support lines could not.
I hope this specific guidance finally clears this up for you. If my answer resolves your issue, please take a moment to mark it as "Accepted" 🙂. This helps others in the community find solutions faster.