Your account is already created. You need to confirm that you are the owner of the email address associated with your Student ID and Codice Persona, which is <codicepersona>@polimi.it.
We use an external service (Google's ReCaptcha) to display a captcha. In case of issues, try to add an exception for this domain to browser extensions such as NoScript or Privacy Badger.
You will receive a confirmation email from us, which your email provider may classify it as spam. So, make sure that you check your junk email folder.