Would you be annoyed?

My ex and I separated in September. We have a 1 year old together. My ex was abusive, and still continues to be. It’s been a horrible break up and so much has happened. I’m struggling with members of my “family” still engaging with him on social media. Calling him “mate” and being super friendly. They don’t know the ins and outs but they know it’s been a horrible situation. Am I being unreasonable when I get annoyed about them contacting him? They have absolutely no reason to do so. I keep my communication to an absolute minimum. So it really frustrates me when my family go behind my back to speak to him. I also know my ex would get an absolute kick out of knowing my family are talking to him. Especially when his family have washed their hands with me completely because I spoke out about what he had done to me and they didn’t like it.