I know it's hilarious to be mistreated by a customer. But sad to say, there are customers who are "always" mistreating the reps. I have been a customer rep for several years and I have dealt with a lot of mean customers.
As though it's the rep's fault if something happened to his/her account. Anyway, call center's number 1 rule is NEVER to mistreat any customer regardless of the reason. That's really a zero-tolerance violation. You get fired right away if you're caught doing the action.
But customers should also remember that these are also humans. Bound to commit errors just like them.
Link: Answers: Should an employee be fired if they curse at a
