I am having exactly the same date of birth issue, when trying to validate mt BT ID (and check on my bill, as prompted on email by BT).
I enter my correct date of birth, but I get the 'that doesn't match your original answer' error message.
If you're able to assist, that would be great.
I'm sure the guys will have you up and running very soon. They've had a test run with my account, so should know which steps to take.
Just follow any instructions given and you shouldn't have any further issues. I'm able to access my account every time since the issue was resolved.
Cheers BrumLee - they've been very helpful so far, and it seems things will be resolved by tomorrow afternoon.