AT&T Cell phone The lies they tell!!! Nationwide

AT&T will tell you one thing and then do something else. I have 2 phones on the next installment plan and added a 3rd line which I asked to be put on the next installment plan. I was told that my bill would be $20 cheaper than it was before I added the line. The 1st month, my bill was lower. The next month it is was $20 more than my bill before I added the 3rd line. I called to did out why my bill had increased instead of decreased and was told that I was put on a contract and there was nothing they could do about it because it had been over 14 days. Well, if the person would've done their job and did what I asked them to do, there wouldn't be an issue. I'm thinki about cancelling all 3 line for $295, which is less than 2 payments anyway. Why should I pay for something that I'm not happy with and didn't ask for?