I have discovered - via the website "This French Life" a useful website for those of you who need to complain to various organisations in France.
The site is a mine of very useful information, with formats for letters appertaining to all sorts of complaints - i.e. EDF, CPAM, solicitors etc.
I hope this will help some of you out there who have problems, and need to know where to start and how to write a letter of complaint.