Appropriately enough, the last thing they did was to insist —demand, really— that, in 2018, I fax them my demand. It just so happens that this could have been relatively safe because, after asking everyone I knew for a week (including some venerable hackers), the only way that I found to send a fax was to ask the local branch of the same bank.
Asking them to authorize the transfer wasn’t possible (by showing them all relevant documentation). Asking them to let me send a fax, using their machine, to a sister branch to tell them to authorize a transfer without anyone verifying my ID, was fine.