People who answer customer service lines have to deal with angry people all day.
If you have to call them when something broke and you’re angry, don’t be mean to them. It’s not their fault the thing broke or that the company did something unreasonable. Being mean to them will not get revenge on the company, and it will not make the company suddenly realize that they have to start being reasonable.
All being mean will accomplish is making someone’s else’s day worse.
Remember that there’s a person there on the other end of the line, and that they’ve been dealing with the brunt of frustrated angry people all day. Don’t be a jerk to them.