Forceful resignation over oral threats

I am writing this after 8 months of when this happened. I was working at a startup (one of the top in Bangalore - not sure if I should name and shame). Little late, but I wanted to call their bs out. I was working my ass off but the company has problems like micromanagement, bad hiring (my manager hired 2 people for same role, when other teams had 1), and lack of accountability (so put the blame on a scapegoat). They have done this before.

Bad part: Got informed in the morning that I won't be working in same team and to look for a different team or resign. When I said no, they called HR for a meet in afternoon, HR threatened me that they can call out performance issue in future bg checks, said they want instant resignation, will pay 2 month notice but take away joining bonus which was a good part. I got scared by this argument and accepted. But now I feel it was a really bad deal. .

What followed was a long spell of unemployment. In their FnF, it is mentioned they have given 2 month notice pay as "severance pay" and I have written mail where I mailed that I want my notice to begin from next month (because I wanted to take time). But they revoked all access to systems.

I wish I could do something about it. This company is known for such practices (and the HR is so skilled in this). Any thoughts?