Azure Signup : We’re unable to validate your phone number

Question

My Azure OpenAI subscription validation process is unable to use the phone numbers I provide to send me the required validation SMS.

The response is invariably 'We’re unable to validate your phone number', regardless of the form of the number used (with or without the country prefix for France).
Yes, I use valid phone numbers, and my postal address actually exists. I triple checked.

I called the support numbers listed for my country but the bots seem unable to provide a satisfactory solution to my problem, and I can't find a satisfactory answer in the Azure forums (although it seems that many people are experiencing the same problem in many countries).

The Microsoft account I use to sign in to Azure is validated using double validation, and I am signed in to Azure all right, only the subscription to the Azure service plan (be it Free or Pay as you go) is impossible because it requires an additional authentication.
I never could reach the stage of payment card validation, which comes next.

Thank you for your help