Problem after interrupted backup

Using Deja Dup, I think. Whatever the program is in Ubuntu System Settings/Backups.

I made the mistake of shutting down the computer to a USB2 drive while doing a full backup. No problem, I sez. Just delete the files and back up again. But, in spite of lots of new duplicity-full files, there is no signatures or manifest file, and Deja Dup tells me the last backup was done 44 days ago.

So I reboot, and it still tells me the last backup was 44 days ago. OK, no problem. I look at the duplicity manual, and it tells me
duplicity cleanup --force file://media/mylogin/MyDevice/path/
(which may or may not solve my problem).

So I try that and it tells me
Local and Remote metadata are synchronized, no sync needed.
Last full backup date: none (none?!)
GnuPG passphrase: Mylogin@MyComp:~$ cd /media/mylogin/MyDevice/path/

How wonderful. Deja Dup is giving it a passphrase? Or what?

Suggestions? Somehow I need to get Deja Dup on track again. I have about 350 GB to back up, so it's not so easy just to start wiping stuff and experimenting.