I know you've tried just about everything possible today. I'm sorry if I'm just repeating what you have already tried. I just want to see you victorious.
I had to do it on my desktop. Couldn't do it on my phone. I logged into MDE on my desktop, and then selected special events on the main page.
https://disneyworld.disney.go.com/en_CA/tickets/events/
Being in the UK, your page may be different? When I went to the UK site, it took me to the same looking screen / web address for special event tickets:
https://disneyworld.disney.go.com/en_CA/tickets/events/
I just know that mine showed no dates available yet, until I logged into MDE first - on my desk top. Then it defaulted to the only date available during my booked trip.