Your account has no registration number

We have been getting this error in our "Billing Accounts" section in admin center:

This is despite the fact that the TaxID numbers are very much entered and visible. For a while this was not posing a real problem to us, but since last few days we are now unable to add licenses and/or subscriptions to our tenancy. The "buy" page now asks for the TaxId and does not accept the ID throwing an "invalid taxid" error

We have a support ticket open since Jun-2021 and there has been no resolution as yet. All my attempts to reach out the support team have been futile. No phone. No mails. No response. No escalation option to customers. No complaint mechanism for customers!

Now, this is a service-level disruption as we cannot add licenses/subscriptions for our users, and for last two days I've been desperately trying to reach out to the support via admin center, phone, Twitter, and what not. But, they are just not responding.

My purpose of posting this rant here is to see if anyone else has run into a same/similar problem, or in the hope that someone from Microsoft sees this and helps.