Whichever country they may be from is no excuse.Are they not used to uk wiring colours?
Blue as neutral is a standard throughout Europe.
The neutral bar has a big blue label above it.
The neutral bar also has a big blue wire connected at one end.
Even the most basic of tests would have indicated things were very wrong.
The only way to make that mess safe is to remove the main fuse, then throw it away.
Or do a Blues Brothers elevator style repair on the whole thing.