The vet probably thought it was not necessary, as above.
However, if you have a bad credit rating with them and can't show the 'readies' than they have every right to refuse. Not saying you're one, but they get plenty of people who try it on and play on the Vet's compassion.
I don't believe a vet is under any legal obligation to perform any treatment on any animal. However, if their refusal is seen by the veterinary authorities as unnecessarily unreasonable or cruel, and is occurring on a regular basis, I think they can be struck off the vets' register.