that is horrible customer service to say the least... and i agree with the OP in not wanting to go back there. They are the experts, if we don't know all the right questions we get screwed? No it is the duty of a responsible service provider to accurately represent the cost of any service.
If I carry my car to service and they say they need to change something i'll ask what it costs to change. They then give me the cost of the parts and the labor and also say well if we change this we would need to, for instance, change your oil which would cost such and such. If they happened to overlook something, before they actually do the change they call me for confirmation.
very very poor customer service, i see nothing wrong with what the OP did