Nowhere. You knew that didn't you? I've just been explaining to someone that I've got a problem with a supplier and they have had delay after delay. I could get angry or accept that it is what it is and deal with it. What would me getting angry actually do? A momentary release of pent up annoyance I suppose but would it help the situation? Probably not. The supplier might just refuse to sort things out or walk away. That's not what I want, I want my goods.
So get rid of your anger, think it through and approach it in a way that they will feel that they will be able to finally deliver for you. They aren't being obviously obstructive, they are sorry that things haven't worked out as expected and so I can work with them or we go and have a fight.
It;s easier to make your point and then solicit cooperation to actually get to where you want to be. Both parties "win" so to speak, a Win/Win situation. Whilst it isn't ideal, it promotes good will and what do you ever get by being angry or having some sort of altercation? You just get entrenchment and disillusionment, resentment and the like.