Rear lower break lights and rear window demister

The above are no longer working we have checked the fuse but still no joy, we had a towbar fitted professionally Dec 06.

They have worked because i have followed my husband home in my car, if he puts the reversing bulb into the holder it works, brakes bulbs are not faulty.

Does anybody have any ideas what has happened?

Ally

shouldnt work, there a double filament for sidelights and brakes, reverse is a single filament
I would try bulbs first, mine went together