Meal worms are lousy food. If you can get superworms he should eat them as well. Get the smallest ones. Keep trying with the crickets, offer dubia roaches, silkworms, and hornworms. He will eventually take to some of them.
The red light at night is not good for him. He won't get proper sleep. If your house is colder than 60 at night get a ceramic heat emitter instead.You should have a basking branch for him that has a temperature of approx 85˚F while he's little 90-95˚F when he's older. The branch should be 8-10 inches from your lamps.
Have you read this info yet.
https://www.chameleonforums.com/care/caresheets/veiled/
If he continues to do poorly a taking fecal test at the vets would be a good idea. Parasites could be slowing his growth.