2002 Renault Laguna rear doors won't unlock

Following a severe rainstorm, the main fuse box became soaked, causing the car electrics to go haywire (dashboard lights flashing, windscreen wipers and washers working etc) whilst switched off.

Approx £600 of repair work was performed by an independent garage and a Renault dealer working in collaboration.

However, one problem which proved intractable was that both rear doors had become permanently locked (presumably due to a malfunction of the child -safe locking system) Bizarely, if one of the front doors is left open when setting the car in motion, an autodiagnostic warning is declared for the two rear door locks as well as the open front door ...........but otherwise the car runs as normal.

We were quoted a further £600 to attempt (repeat attempt) to fix the problem
which we can ill afford.

Could someone please advise us.