im sorry but your guy needs to see a vet at this point. you have been misled by the pet shop. im going to list a basic care guide for jacksons and possible solutions but again i would take him to the vet ASAP.
1)check for parasite - this needs done asap for both chameleons. most jacksons are wildcaught.
2)correct your temps
3)correct your uvb bulb
4)give him as much misting as as you can at this point. in your water bottle get warm water from the tap and fill it up and spray. hopefully he will drink.
5)slim down on the d3. he doesnt need that much. implement a good gutload regiment.
montane species (cool and humid)
Cage:24x24x48' SCREEN cage lots of rope, vines and live plants if you can. live plants will help with the humidity. make sure you cover the soil with screen. put cage as high up in the room as you can. not near any vents, fans or windows.
Lighting: 5.0 reptisun or reptiglo linear tube (length depends on cage size)/house hold bulb for basking. the house bulb watt will depend on how far your nearest branch is from the light and your ambient room temps.
***change bulbs every 6 months.
Temps: basking temp around 78* / ambient temps 72* measure by digital guages.
Hydration: manual spray 2-5 minutes/2-3 times a day. provide a dripper.
Feeders: gutload (24 hours before feeding) with fresh veggies and fruits and once a week with sticky tongues gutload. Crickets, mealworms, superworms, silkworms, hornworms, dubai roaches, reptiworms, BB flies.