If these steps don't work -- and they often do not -- you may need to take action on your own or through a lawyer. In fact, if you suspect the brokerage firm is guilty of fraud, or the matter is important, or substantial sums are involved, contacting a lawyer early on, and not delaying in the hope that someone who has no particular motivation to help you, will do so, is the wisest course.
When a lawyer gets involved on your behalf the brokerage firm often will pay greater attention, particularly when the lawyer is experienced in broker disputes and/or securities law. Based on the facts, the lawyer might also tell you that you really do not have a claim, in which case you could stop getting yourself upset about the matter, or seek another opinion.