Yelling at the low level people at the end of the phone is easy, but it accomplishes nothing positive. Those people get their info from the managers. The managers are safely protected from your screams behind their sound insulated office doors and walls. They only care about getting the sale and are willing to sacrifice their end people's ears in order to get them. Those people at the end of the line having to interface with you actually can be very helpful when they are happy, but when frustrated by rude callers they can turn sour and unhelpful very quickly. Eventually they will probably quit and look for a different job after which they will be quickly replaced by the next innocent drone (or replaced by a fully automated phone answering robot). Again, all this happens while the managers listen to music and rest their feet on their desks happily planing their next vacation.

So, if you really want to make a point that makes a difference, file a complaint! Yelling to the phone people is brainless.