How Can I Get A Result When I Make A Complaint?

When complaining the one certain way of alienating the service provider is through being too pushy and aggressive.  People seem to think that the only way to complain is to shout, bully and intimidate until they get a result.
However, a far more effective way is to be incredibly polite.  The 'I am so sorry to trouble you' route.  Charm your way into getting a result !
Outline your complaint clearly and concisely.  Do not exaggerate, nor should you be rude.  Explain what the problem is and ask what action will be taken.
If the suggested action is not good enough for you, then take your complaint higher.  In person ask to speak to a more senior person, if in writing, copy your complaint to a more senior manager.
Be quietly assertive, keep repeating what your issue is and that you expect the issue ot be resolved.  If you are still not getting anywhere, then you should (politely) state that you feel you have now been forced to seek legal redress and express your regret that they could not have handled the situation more competently, which would have avoided a potentially lengthy and very costly case of litigation.