Finally I find a way to join GoPro and it works very well !
I didn't tried all the way to join them, I forgot about...smartphone. No comment. Maybe I am oldschool, trying to stuff on "computer".
So, by using the formular of the gopro website (on Chrome on android phone), I finally was able to chat with somebody.
They ask you about your problem, send you an email with a link to upload files (photos + order), you have to wait a few minutes to have an answer. In my case, they offer to replace the camera (I received stamps on my mail box). Send the old and receive the new took less than 8 days. The person I talk with was very professional.
Conclusion: still: why it just don't work on a computer ?! and once you found to join them, the service is correct. Sorry for sending a bad advice when they asked me, but, the process was really difficult.