It won't be....but hang in there. See if you can get more from them for the trouble.
You were right, my May bill is wrong. So, I googled executive customer relations, and found a phone number to call. They took my name and number, and a few hours later someone called me back. She had reviewed all the notes on my account (I'd called roughly 16 times, spending an average of 30+ min per call), and found confirmation of my promised lower rate. She said my bill was supposed to be fixed effective this month, and could not say why it wasn't. She opened new tickets with billing and with IT to review the problem. She told me she would personally be monitoring my account and gave me all her contact info. I think she may finally be the person to get this fixed.
She gave me a credit for the amount I was overcharged. However, when I logged in yesterday to pay my bill, I had a negative balance. I'd gotten an additional $140 credit. I'm not sure if the executive rep did that, or if it's a result of one of the tickets she put in. Either way, I'm not complaining!
Remember not only to say the right thing in the right place, but far more difficult still, to leave unsaid the wrong thing at the tempting moment.