Terrible Customer Service plus Extra Charges

I have been ATT customer for 6 years. Last month, I called ATT to discuss my bill and data plan options. We have family plan, so the rep recommended 10 GB for additional $10. I got my bill, and surprise, surprise, my bill is twice as usual. I did upgrade to the new iPhone, but no one told me, that first, now I am paying more monthly for data, and secondly, because I upgrade mid month I have to pay for both plans ???!!!! ( that's what the rep told me, while giggling and repeating my name 100 times,-  she couldn't even explain the bill to me). When I asked to be transferred to different rep, and I asked her would she pay for something she is not using, she told me absolutely not, but yet, I am charger for something no one can explain. That was very shady on ATT, and customer service should be your priority, clearly it is not. Very disappointing.