Always ask if the have experience with reptiles and follow up with experience caring for chameleons. Most vets only deal with mammals and "exotic" vets care for anything from birds, more uncommon mammals, and common reptile species such as bearded dragons, snakes, geckos. Chameleons sometimes have health issues that are unique to them such as tongue problems. Tongue related issues can be caused by several underlying problems such as nutrition, injury, vitamin deficiency, and so on.
Chameleons are also notorious for hiding symptoms and appearing healthy from a visual stand point. Sometimes blood work or x-rays are needed to reveal whats going on inside their little bodies.
Don't give up on your search for the right vet. Always ask if the vet you called have any recommendations if they do not possess the experience to care for your cham.
Hope you find some solutions for your buddy