Trimming teeth is something that needs to be done at the vet since it requires the proper equipment and training, often times they need to sedate the chin unless it's just the front teeth and he is very cooperative. It sounds like you found a bad vet, so you likely will need to look for another, if they did x-rays tell them to send the to the vet you find that can treat him. Did they even say what was wrong with the chin? Or were they unable to find anything wrong? What are the symptoms? A problem in the mouth could be all kinds of different issues, it could be a sore in the mouth, it could be over grown teeth, a tooth spur, a cracked tooth, or even something stuck in the teeth. If he can't eat you may also need to be hand feeding him, either get some Critical Care food or grind up some pellets in water and syringe feed him that until you can get to a vet that can or will treat him.
