Employer and employee conflict of intrest

I started as consultant marketing registered under my dad name sourced customers and was giving to trader through his employe .were I dont have any contract with trading company . And trader was unaware of such. But I was charging my comission from client end and earning my margins. Later I got hired by same trader as employee and business grown at both company. But trader now my employer doest know about paralel company of mine .recently I resigned that job and my previous employer threatening me to share the details of consulting firm or will sue you.like invoices raised And he has some invoice of my firm retrieved from my employer mail I'd. In invoice my phone number is mentioned and adress of firm is my home adress N in some contracts I used word as employer name and its associates . Some mails have been exchanged from employer I'd for sharing invoice . But in all cases same client pays comission to both