The person answering the phone may be the first person willing to help, not the person who caused it.

Frustration lands on whoever picks up, and that is almost never the person who made the decision you are angry about. The policy was written elsewhere, the delay happened upstream, and the voice on the line is simply the first one that answered. Spending your anger there mostly makes them less able to help you, since people problem-solve worse while being shouted at; aiming your energy at the problem rather than the person usually works better.

Open your next difficult call by saying what you need and that you know it is not their doing. Save the escalation for someone who can actually change it.