Your ex would not need to know your account number to do this. You can set up a blind account number (sort of like how you can with Visa when you online shop).
I read what you stated previously about the checks coming later and later. Maybe he is going broke, maybe he is f'ing with you or maybe he is just a first class ass. There really is no way to know.
If he is not following his legal obligation you know what to do. My H contacts me when he has a fight with his mistress, is board, tipsy or feeling guilty.
They do this because they are hot messes. And yes, "hot mess" is the technical term!
