I have 2 questions: Is it possible to add data plan by using the available balance on, say $100 GoPhone card? Can I buy data plan for selected non-contiguous month of the year?

It was my understanding, too, that the data plan could canceled at any time. I canceled it by calling 611. Still, AT&T took another $45 out of my balance. I can't reach anybody. How do you make sure the thing is canceled? How do you stop the charges? Does anybody know how?