Still can't renew Free Substance 3D for Students and Teachers License: "UniqueID already exists"

One year later, same problem.

I tried to renew my Free Substance 3D for Students and Teachers License by submitting a new request for an e-mail with my Adobe ID. But this mail was never received and no, it isn't in my spam folder. I can't resend the mail, because I now get the error: "UniqueID already exists" in the forms input field. I tried my secondary e-mail address, but that didn't work either. 

Why is this still not fixed and how can I renew the license anyway?