Upgrade has lost all settings and emails.

After the holiday break emClient loaded an upgrade and at completion of the upgrade had no accounts or data in the system.
As far as I can ascertain, there was no question about data migration but we did Menu - File - Import… - Import from eM Client 6
It brought in the two accounts (POP3) but no emails related to them. It loaded the data that was waiting for download, but that is all that is there. Old all emails are missing.
I have checked and the mail_data.dat file is 53GB in size but we only have the 50 or so emails visible.
I did a backup and it is only a small file, so obviously the 53GB is not being backed up.
So, I assume my emails are there but maybe/somehow not visible.
Can you help me as I need these emails

P.S. I do have a backup but it is a month old, so I was hoping to try and recover all the missing data.