Harassment (unfairly harassed by two Managers)

I feel I was unfairly harassed by two Managers I worked with from the date I was hired. They obtained testimony that I had given the appeals judge (in confidence) at the unemployment appeals board (to collect benefits from my previous employer), and told other employees in the firm about it. The information has resulted in defamation of my character and name calling. When I reported what I had overheard, I was told that harassment wasn't allowed at the company, and that I must have misinterpreted the conversation. Would an attorney be able to obtain the original source of the information, if it's an email, or would I need witnesses to testify? At another time I overheard a death threat made against me and reported it. After that I was told to work at home, and then was terminated a few weeks later.

I signed off on a severance package, because I was told I only had 7 days to review and signoff in order to receive payment (I'm over 55).

Do I have a case here?

An attorney could subpoena and documents or emails etc.

But you need actual illegal acts; mere unkind words and the like are not enough.