Start compiling all the data on paper. Have the dog treated at a different vet and then send the ex-vet the bill.
When I worked at a local vet(and probably the worst one in the area, honestly) we even knew to put even "questionable" dogs in ISO(isolation), this meant any and all dogs that came in from the animal control or dogs suspected of parvo.
You have a right to be upset. Keep at it, parvo treatment is expensive, but it is a survivable disease. I have known dogs who survived TWO attacks of it and survived into adulthood.
Please, please, please, make sure this vet pays for this and that you report them to the authorities, that is a HUGE breach in protocall.
-Kim