Kinuta's right. Change vets now. If there's a specialty cat clinic anywhere nearby, try them.
Years ago, I got a cat through something similar by making her a sort of t-shirt from an old tube sock. Cut off the toe of the sock, cut two leg holes, and apply to cat (a two-person operation).
That mysterious kitty injury, BTW, turned out to be a burn that probably came from sleeping next to a radiator.