WhatsApp Restore issue

Hello,
When I installed WhatsApp, it didn't find the backup at all, instead starting straight after verification into the app, with my chat groups present but no messages. I tried renaming the backup file to the standard database file and reinstalling WhatsApp. This time it found a backup, but listed it as 0KB in size and dated 1970! Choosing to restore this backup didn't work - it failed after a couple of seconds of processing with a message saying sorry, we can't restore your messages.

Any questions I've already come across tend to suggest copying the entire android_storage directory. I did also try copying the entire WhatsApp directory from android_storage to the new phone, but it still came up with a backup of 0KB from 1970. After trying so many times (and reverting to my old phone to re-make the backup file), the WhatsApp verification step has blocked me for 13 hours, so I'm very limited in what I can try now.

Is there anything I can do to get my messages over to my new phone? Is the 0KB and 1970 thing a clue towards some sort of issue?