Disappointed

I got an iPad mini 2 ..say it was free for inconvenience ,and it was said pay for 36 for tax plus 45 for registration . Plus $10 every month 1gb data. I was like okey cool. When I cancel my data because I have unlimited plan. I never used it . Thinking it's a waste of money they charge me $146$$$ without letting me know about it. I called them saying they don't have the right to give me credit if they would they gonna do it. Shut me down 3agent because of same issue. Why they don't explain carefully what's on.. because they want me buy some stuff from atnt? Which is I don't need it.?. Seems I bought an iPad more than a regular price .