What recourse do I have against a former employer who is contacting my current employer about me?

I worked for a medical practice that was run in an enethical and unjust manner. An employee was fired for seking reimbursement for being clocked out for lunches she was unable to take. The remaining front office employees were fired for not agreeing with her treatment as well as other office conditions - myself included. I found out the same day I was fired from the practice that I was accepted at another practice, so I did not pursue legal actions for being unlawfully fired. CA is an at-will employer, didn't seem worth it. I did however, file with OSHA regarding blatent violations, as did the 4 other employees who were also fired.

Fast forward a year and a half and they are buying the building where the doctor I work for currently practices. We got some of their mail and my boss emailed my former employer to see what they wanted us to do with the mail. My former employer responded with a statement saying they were going to install locked mailboxes, additionally security cameras, and additional lighting in the parking lot to assure there would be no mishandling of mail or damage to their property or vehicles due to "a former employee's threats against the property." I am their only former employee who works here, so they are obviously talking about me. Additionally, they informed my current employer they were willing to discuss "the employee in question" in a face to face manner regarding things that would shock my current employer. My employer is unwilling to participate in any conversation without my involvement and HR's involvement, but it does not take away from the fact they are influencing my current employer in a negative way.

My former employer states they have written proof of my threats to the building, which is not possible as I have had no contact with anyone from their office in almost 2 years - and I have not emailed, text, or discussed the situation. I feel harrassed by my former employer and I am not sure if I have legal rights here. I know it is not legal for them to say anything negative about me if they are asked by a perspective employer, but do I have rights if they are seeking to inform my current employer? Thanks!