Sorry to hear you can't get a solution to this.
First question: does your company already have an Azure subscription? If yes, you don't need to create anything. Whoever administers the existing one can grant you the Artifact Signing Identity Verifier role and you can work from there.
If there isn't one, the Gmail attempt tells you something. If your domain were the trigger, Gmail would have worked. It didn't, so it's something tied to you rather than the domain, usually the payment method, phone number or IP used at signup.
You're right that a personal account won't get you there, and the reason is worth knowing. The Quickstart says individual developer validation is limited to the United States and Canada, and the billing account type has to match the validation type, so a personal billing account can only do individual validation. Even where it is available, the certificate carries your name rather than the company's, which defeats the purpose for company software.
And the FAQ says Artifact Signing "doesn't support free, trial, or sponsored Azure subscriptions". If the signups you were attempting were free or trial ones, they wouldn't have served this purpose even without the block.
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