Yes I would definitely keep track of all calls (time, person you spoke with, and what was said) and have records of all vet bills. Because if need be I would go to small claims court, because at this point it is more of the principle of the matter and him taking responsibility for his actions. I'm sure he would be furious if this same situation happen to his beloved small family member, he OWES you an apology and payment of the ER bill at the least.
I'm so very sorry you have to put up with such nonsense. People have to know that if you are providing a service to other people you have to give 200%, its not an option. How you serve others is a direct reflection of the kind of person you truly are. You give the best of yourself no matter what.