The law does not require that you receive notice, warnings, or write ups; there is no law requiring that they do an investigation.

Wrongful discharge does not mean what most people think it means. It is not a wrongful discharge unless there is a specific law that prohibits the employer from terming you for the reason they did. EVEN IF company policy requires that they do so, violation of company policy does not make it a wrongful termination.

Sorry, but your recourse is to file for unemployment and look for other work.