Never, ever trust auto-renewal. Doesn't matter if it's with Admiral, or Direct Line, or the AA: Always, always, ring them up and speak to someone.
In all likelihood if you'd been stopped and this had gone to court, you'd have been okay with what the bank has told you, but that doesn't stop it being terrifying anyway. I tend to check AskMID every week for all my vehicles, just to check. Takes 30 seconds and whilst overkill, does put my mind at rest.