I was falsely accused of Blackmail to ensure my dismissal do I have a case?

If the two executives knowingly made false statements of fact (not opinion) about you which caused you damage, they have defamed you (libel is written defamation, slander is oral defamation).  If they lied about you with the intent of getting you fired, and you were fired as a result of their lies, they have tortiously interfered with your employment contract.  You can sue the executifves for these torts, and possibly other causes of action.  Litigation is expensive, however, and there is never any guarantee that you will win.