The old company in liquidation is now called FBE Realisations Ltd and those with a claim need to file it against that.
The new Flybe 2.0 was originally called Thyme OpCo before renaming themselves after the old Flybe became FBE.
Legally, you wouldn't get very far with any claim you had for the old company against the new one.
It's not overly different to football clubs going bust and the company registered at companies house changes names whilst the name of the club continues.