How long do you wait between feedings? You said at the start you waited three days, simply not enough. If you have a refusal of a meal, you try again 7 days later.

Trying too often will just stress him out. Don't handle him at all until he eats.
Try leaving it in over night. Try filling the tank with newspaper (in balls) to give lots of hiding places.

Tons of things to try, he's still young, but that doesn't mean going 4 weeks without food will harm him. Be patient.