Cell C trying to force me into a contract

Cell C contracts department wont allow me to cancel my one contract that's due for an upgrade, it seems to me like their forcing me to keep paying, or take the upgrade of which I am not interested, every time you ask to be transferred to the cancellation department, the number cuts off, if you call yourself directly they don't answer, my contract ends in May 2019, if this cancellation does not go through and they continue debiting I will reverse the debit and also lay a complaint for theft with the authorities I am tired of Cell C taking advantage of me as a customer