How do I change my Security questions without phoning apple?

the last few days I've been trying to purchace some music through iTunes I however can't without answering security questions. It's always slightly differnt questions but one which I don't know the answer to. I know the answers to the others. I've been trying to get an e-mail from them to change it but it never comes through and it seems like my only option is to call them which I don't want to do.