It will be hard to give you specific advise because I/we can't see your mistakes and work with you first hand. But don't worry you are not alone. Don't give up, it's worth all the pain and frustration.
Question. Are you afraid or uncomfortable in you're toe edge? Most of the people with your similar problem that I have helped could heel edge all the way down the hill but would avoided using they're toe edge due to a couple fears. Fears I recall where. Back facing down the mountain and not being able to see. Catching a heel side edge taking a hard fall. When in toes edge they were not confident about being able to maintain edge control or keep the heel from dropping which causes a hard fall.
So before I allowed them to try J turns on they're toe edge I would make them as followed: start on your knees pushing yourself up into your toe edge, then staying in your toe edge the entire time getting familiar with edge control keeping the heel edge up, knees bent, good posture, pivoting your hips makeing the board go right then slide with control pivot hips back left with control while in your toe edge allllllllllllll the way down. You are not allowed to move past this step and must keep doing it till feel just as confident as your heel edge does. Almost everyone by the 3rd or 4th run of nothing but toe edge they became toe edge masters. And then move forward to J turns then wide links.