I understand the frustration and have had similar experiences.  I get so angry I want to just shake the person, knock some sense into them.  But that may more about me.  Sometimes it helps to write a long letter, write everything  I need to say ( helps me vent, like cheap therapy) then I edit the letter only using the strong key points. 

I always have to keep in mind the main objective is the wellbeing of my child not how angry I am that they can’t do there job right.