After not getting any responses to any other methods (including signing up for WhatsApp and sending a message there), I wrote a short e-mail to Henrietta Alexander and within a minute received a response and a link with which to submit my negative test result. Thanks to her and everyone here. Now it just needs to get approved, but that should not be an issue.

I really wonder what happens to poor folk who only use the official e-mail on the site for their questions. They probably end up missing flights.