ADHD and screen addiction

My husband and I have been married for 13 years and we have 2 kids (ages 11 and 3). My husband was diagnosed with ADHD last summer at the age of 36. He was prescribed medication which he took for about 6 months, then abruptly stopped taking it and said he didn't like the way it made him feel. His screen usage has always been a major issue throughout our relationship. When we first met it was video games. He would play every day for hours and hours. Over the years it has morphed to other things, but now he spends most of his free time on online gambling sites buying and selling sports cards. He is an admin in many of the sites and he is literally glued to his phone monitoring the activities of these sites. We have had countless conversations about his screen usage, especially during the limited time we have during the day with our kids (we both work full-time). I frequently have to ask him to get off of his phone during meals or while the kids are trying to talk to us or seek our attention. Not only do I feel his usage is excessive, but I also don't feel he is setting a good example for our children. Our daughter is also diagnosed with ADHD and I want her to be able to regulate her own screen usage when she is an adult. My husband does not see any problems with his actions and every time I try to talk to him about it he always justifies it in some way or it turns into an argument. I am tired of feeling like I come second to a cell phone. Has anyone had any success dealing with this specific issue in their relationship and how did you solve it? We have tried establishing time limits or keeping certain times of the day "screen free" but it never works for long.