Exactly the same thing happened to a colleague of mine. I had put it down to human error (somehow missing the prompt when the 2FA details were first shared), but now having heard that it's happened to someone else, I am more suspicious...
We have a BR Fares organisation account with several different users. I was the first user to set up 2FA, and experienced it as David described with the 2FA details clearly shared. But the second user does not remember seeing any 2FA details being shared until being suddenly faced with the prompt for a code. I am wondering if a similar situation could exist with you? In particular,
I sent a support ticket
How were you able to send a support ticket if you can't log in? Do you have another account?
Maybe I am totally on the wrong track; was just a hunch. In our case I (who had my 2FA credentials stored) logged in and sent a message on behalf of the locked out user, and someone from RDM got in touch and arranged a video call to prove identity and set up the 2FA properly. A slow, clunky and labour-intensive process, but it worked.
Paul