Azure for Students: "You're not eligible for an Azure free account" with a UNED (Spain) academic email

I am a university student at UNED (Universidad Nacional de Educacion a Distancia, Spain) and I live in Ecuador. I also have an active GitHub Student Developer Pack.

Problem: when I try to activate Azure for Students I always get the error "You're not eligible for an Azure free account" (shown in Spanish as "No cumple los requisitos para obtener una cuenta gratuita de Azure").

What I did:

• Signed in with my academic account (domain: alumno.uned.es, a Microsoft 365 / Entra ID tenant).
• Opened https://aka.ms/azure4students and also the "Microsoft Azure for Students" card inside the Azure portal.
• Completed the profile (country: Ecuador, academic email, phone) and submitted it.
• Result: the error page, every time. In the Azure portal this account has no subscriptions.

Notes: I may have claimed Microsoft 365 through the GitHub Student Developer Pack with a different email address, but I have not created any Azure subscription with this account. The Azure Help + support assistant said the cause is usually that the institution's domain is not registered in the academic verification system, or that there is a previous activation.

Questions:

1. Is the domain alumno.uned.es recognized for Azure for Students?
2. Could another Microsoft account with the same name or phone number block eligibility?
3. Who can fix this and how can I contact them, since I cannot open a support ticket without a subscription?

Thank you.