2. DON'T dispute the claim; DON'T re-direct the blame - When the customer is charged and yelling, stay silent. Or verbally "nod", by giving an "uh-huh", "OK", "right", "I see", or some such, whenever they reach the end of their sentence.

3. Don't talk over them! LISTEN. This lets them pour out all their negative thoughts and they soon realize that yelling isn't going to work. Don't say "No, I don't think so, you must have your account confused, our systems simply don't do that". You'll add fuel to the fire by doing this and they'll end up shouting "YOU'RE CALLING ME A LIAR NOW?!!?".

And don't blame someone else - or another department in the company - for the mistake. "Oh gosh, I'm sorry, must be accounting again, they haven't gotten anything right all year".

This makes you and your company look unprofessional and incompetent. LISTEN to the customers problem.

If they continue to yell and scream, using bad language, and so forth, don't say: "LOOK IM NOT TAKING THIS!" and hang up. No.

"Hmm, Mr. Taylor, I really would like to help you. I think it would be a good idea if we talked about this when we've BOTH cooled down". This takes the focus off his behavior.

4. Once you've clearly understood the problem, repeat it back to them in their own words. Write down what they say and underline what's relevant to the situation. Something like this, perhaps:

"OK, Mr. Taylor, I want to make sure I’ve understood you correctly and please correct me if I'm wrong. OK, so what we need to work out is why your account balance is missing a $4000 payment you made last month (their own words), right?"

5. Once the customer agrees with you (you should always ask questions that get a YES response), empathize with them. Not sympathize, EMPATHIZE.

I've heard some pretty pathetic examples of this! People whom you know (just from their tone of voice) don't give a damn about your problem.