Open Question: What should my insurance company do?

Hi, I would like to know what happen if someone rear-ended me? My Canadian insurance company said that I have to call the other insurance as well. But I think they are lying because I complained about their service few days ago. Are we supposed to contact the other insurance company if the accident is NOT my fault, but rather other person's fault? The question is that I think I am NOT suppose to contact the other person's insurance company directly, but my insurance company asked me to contact them as well. It is legal for them to ask me to contact them.