You should be able to see the slots but they'll be showing as booked up/unavailable.
Can you see that far or can you literally only see up until 12th Dec?
If you can't see past the 12th Dec and you had the email saying you could book from today, there's a glitch somewhere.
If you can see the slots for 23rd Dec etc and they've been booked up, then you're logged in OK but the availability in your area has just gone.