okay when you ring them, dont yell at them coz they will get more pissed off and not do anything.
a thing that you can do is really calm voice, but repeat how important it is this is, and keep on telling them if you wont get an answer, you would like to speak to a supervisor.
I work in the industry, and everytime people does that to me, for some reason i always cringe...
Also ask for their ID number and reference number for the conversation, and write it down in case they lie to you...
if its going to the extreme, record the conversation and tell them that you are recording the conversation. It is legal as long as you tell them beforehand