Defenitely not a situation to be in on an exam day. I can unserstand how irked you could be since I went through a similar situation at a visa consulate.
Anyways be positive, focused and once you have your issue sorted out, go back and settle the "score" with Pearson VUE.
"To dream anything that you want to dream, that is the beauty of the human mind. To do anything that you want to do, that is the strength of the human will. To trust yourself, to test your limits, that is the courage to succeed."
- Bernard Edmonds