The benefit of the doubt is free

There is no harm, no foul in giving people the benefit of the doubt - you called and they didn't return your call; maybe they are out of town or dropped their phone in the toilet. 

Sure, maybe someone has done something seemingly egregious, but maybe there was a misunderstanding, or maybe they had your best interests at heart but royally screwed up. 

Putting people on the defensive gives no benefit to you. Blame has no upside - other than not having to actually deal with what is truly going on. Guilt and a defensive response and stature are soon to follow blame. And any attempts at finding a constructive solution to your problem just got a heck of a lot harder. So, take a breath, take some time, and get to the bottom of what really happened before you jump to conclusions and rush to judgment.