What I noticed is that when you start complaining, he probably feels attacked and digs in even harder with his position - happened to me with a girl I dated a few years ago, she was always on her phone and the more I said something, the more she'd get into it. In your case, instead of it being a problem of "time on social media," it's really about you two not having quality attention for each other, and that's legitimate to feel. Maybe it'd be more effective to have conversations about how you actually want to spend time together, instead of pointing the finger at Instagram - like "I want this to be ours, without distractions" - and then you both work out when and how that happens, without it being a top-down ban.