I think you're being too hard on yourself, this type of job is very demanding and even in an office environment without proper training or some similar experience it is very hard to succeed. The people calling at Customer Support are irritated even before starting to wait for someone to answer, and on top of that, a hot-head, it's a hot-head, no matter the circumstances, and he can't wait for the moment to start screaming. Customers are always right full of shit.