I have had great success with

1. Calling Customer Service and recording date, time, and agent. Every detail. Even if the dummy cuts me off inadvertently.

2. Persisting with yet another call and request to talk with a supervisor, get name, etc.

Still no go? I then write to the president of the company with my saga: names, dates etc

It produces miracles most of the time. I just got $200 knocked off my daughter's Cellular One bill because of a lying promo to college students. I had EVERYONE'S name, inc the supervisor who would not call me back. I got one agent at Hertz (she refused to call a supervisor to settle my problem) so mad at my persistence that she finally swore at me. Then you really win. Swearing is not allowed. She got 3 days off without pay and I got a free weekend.