My boyfriend’s friends still support his ex

Two of my boyfriend’s friends still follow his ex girlfriend on Instagram and so does his brother, they also like her posts while my boyfriend has her blocked. I told him I was uncomfortable with this and instead of understanding where I was coming from, he got defensive and basically said he’s never introduced her to anyone (which I don’t think is true) and kept telling me I want to argue when all I want him to do is talk to his friends about this… I’ve followed one of the friends before in the past and he never followed back too so it makes me feel even more uncomfortable. What do I do?