Six months after my PhD graduation, I submitted a paper to an SCI journal as a sole author. Apparently, my PhD supervisor is the technical editor for this journal. He wasn't pleased that I submitted a sole-author paper without informing him. I formulated the idea and wrote everything from scratch. However, he claimed that's a generalization of what he's currently working on. After I proved to him that they aren't related he went ahead to forbid me from publishing in that area as it's likely to interfere with his. That's after he made me divulge all my on-going investigations. He said it's better we are collaborators than competitors. I didn't set out to compete with anyone. Most ideas I gave him during my PhD were suppressed only to be given to other students two years later. He made me the last author in those anyway.
Question: 1) Does he have the power to do this? 2) Being that he sits on the board of top SCI journals in my field, how do I overcome this?