Cancelled contract - still charging me

I was under the impression, that before an upgrade is offered, I could actually opt to stop my contract. I did this in December. <br> <br> I do not, by law have to inform you of the contract ending. This is not a rolling contract. Then, they say that I did a late cancellation???? And still billed me?<br> <br> I want the future invoices to be stopped immediately and all moneys paid back to me. I do not want the money in \airtime\" because I do not even have that number anymore! "