First, let me say that I'm sorry that you've had to go through this situation. It certainly is unfortunate and unfair. Unfortunately, I can't give you good news here.
Due process is a very specific legal concept. It typically only applies to situations where the government is trying to take something away from you. This is why people with government jobs are permitted due process of law before termination. People that are having property or their freedom taken from them by the government are also entitled to due process.
But that entitlement doesn't extend to private employment unless there are specific provisions in place to make due process required. Most employment in this country is "at will
." That means that it can legally be terminated at any time, with or without warning or due process. It can be terminated with or without cause.
For a person to be entitled to due process prior to termination, they would need a contract of employment stating that they can only be terminated for cause or they would need some sort of strict company handbook or policy requiring due process before termination.
Otherwise, no length of good service can create a due process requirement. No reason (aside from very specific discriminatory reasons based on race, religion, gender, age, disability or FMLA
use) would be considered illegal.
In this situation, without a contract, handbook or company policy, the employer doesn't legally have to prove that you deserved termination. They simply had to not make their decision based on one of the few illegal reasons I mentioned above.
On the facts you've given here, the decision was undoubtedly unethical and unfair, but that facts don't support this being an illegal termination.