How can you protect yourself from being falsely accused of breach of confidentiality

Over the past 2 years I have documented hostile and discriminate behavior against me in my workplace. It got so bad that one-day the Director exploded in an anger and rage against me in front of the entire office. I documented the event and sent an email to the HR department. The retaliation I experienced was awful, they took my sales numbers away from me, which lowered my take home pay, and they intimidated the entire office that witnessed the threat against me. I worked under extreme hostile conditions for too long and left 7 months after the assault, to work for another company in the same industry. My old company has sent threatening letters to my new employer and me. And because non-competes don't hold up well in the sate of CA, they have begun threatening and wrongfully accusing me of breech of confidential and non-solicitation as another way to harass me. The company has a very bad reputation in the furniture industry because of their quasi-unethical and litigious actions. The new company's attorney has begun communication with my old company's counsel, and are willingly to negotiate. However, the old company has drafted a new agreement asking me to sign a mutual release and they will leave me alone, I don’t trust that company what can I do?