Get a lawyer. Sue them with the ferocity of a liberal at a welfare office.
You likely cannot sue - I’ve never seen a brokerage agreement that doesn’t have an arbitration clause. So you will be playing against a stacked deck. If you do invoke arbitration, you need a lawyer who knows what he is doing with an arbitration case - there’s as much work preparing for an arbitration as for a major lawsuit, and the broker’s lawyers are going to know every rule and trick (and go for an arbitrator that wants their repeat business).
You do want to mention that you are willing to get their regulators involved (FINRA or the SEC).
But if they can’t get it straightened out by Monday, you need to find a lawyer 1)licensed in your state, 2)familiar with securities law and 3) knows their way around an arbitration. This won’t be cheap.