Throw truth darts. What did you really say to your niece? What could be construed as controlling? Your wife is projecting some, she is controlling you. Your STBX is still filling in the blanks (mindreading.) She's playing the victim here, remind her she has a choice that she can talk to whoever she wants.
W's parents communicated with me regularly for 8 months during the separation. Once she filed for divorce, they dropped me like a dirty shirt. No communication at all since then. It did hurt my feelings that my neice still was 'friendly' with my W, especially since now she is trying to take the kids away from me. I communicated this to my neice.
I want my W to know that I still care, regardless of her projection that I didn't and don't!
"Always go straight forward, and if you meet the devil, cut him in two and go between the pieces." - William Sturgis, clipper ship captain, 1830's.