Youve got off to a bad start in this company, not your fault. People in charge of others should always handle staff carefully, they automatically have the superior stance due to their position so when they are too harsh for the situation its a sign there may be problem. No one in authority needs to flout it.

As you have only just started its not wise to confront them about not being told and wanting to see proof you were. From here on to keep this from happening again ask for them to ensure that instructions/requests are explained and are signed for/over so that you can be sure you remember what you have been requested to do. Tell them its because you want to make sure you dont mess up again, that you were very concerned about this incident...its not that at all, its so they cant lie again. Do this via email to your superior.