Hi João Colbano,
Thanks for reaching out to Microsoft Q&A.
Make sure the emailid, credit card and other details are not used before. If he doesnt have a school email he can use a personal email account to get one time 150$ free credit for 30 days. Are you aware of this and looking for something else?
Please 'Upvote'(Thumbs-up) and 'Accept' as an answer if the reply was helpful. This will benefit other community members who face the same issue.