Sounds like your ego got the best of you. The person made a mistake, and for it to ruin your day because she didn't confirm your correctness means that you should learn more about the ego. So much of our daily interactions revolve around our ego or that of others. Maybe the service person didn't want to admit error because of their ego and it triggered yours because it transferred to you. In the end, it doesn't affect who you are as a person when something like that happens. We expect too much of one another and often not enough of ourselves. Be the bigger person and rise above.
With that said, we've all been there and let it get the best of us. I used to get super upset over things like that. Reading A New Earth by Tolle really helped me to take a look at such interactions. We're all having a shared experience and that person fell short. That's an opportunity for you to pick up the slack.