The other tip I heard (which has worked for me) is to say something like "I need help to ask the right question, because I don't know how the process works. Here's what I want; what do I need to do to make that happen?". This is more for bureaucracy but also works for some customer service stuff.
As someone else who worked in customer service, this is very true. There is a lot of stuff we're not allowed to offer, but if you specifically ask for it we can give it to you. So please, ask questions, and be polite. No one calls customer service to say "everything I bought works perfectly and I'm happy with you and your company. Have an awesome day!"
I dealt with angry people just about every second of every day. The job has huge turnover for a reason. Please remember you're dealing with your fellow man, and even if you're angry, it's not (yet) his or her fault that you are.
