Worked as a contractor for a company. After terminating agreement, I contacted other contractors that worked with them.

I had repeatedly requested that the company stop emailing me after we terminated agreement. They proceeded to email me with a list of other contractors whom I contacted, asking to work together/socialize with them. I also made them aware that while they were being paid $30/hr, the going rate the company was charging was $120 hr etc. The company's lawyer keeps contacting me saying I should get in touch to take care of the damage or they will take me to litigation. How serious is this?