I would contact both your BBB and the American Veterinary Medical Association
http://www.avma.org. If this vet really completely misdiagnosed and was not providing appropriate care they might have a complaints department. When you go to the Humane Society, let them know about you troubles with the vet. You don't want them referring people to him.
It is so sad when something like this happens. The vet I had for my first dog refused to do preventative worming, and the little puppy got such a bad case he almost died. And when we switched vets, the new place said they had tons of complaints about him! I am sure you will find a wonderful kitty at the shelter who needs all the love you obviously have.