No permission given to upgrade an account / Contracts closed

I had 3 contracts which was cancelled in writing in August 2017 as the contracts expired in September 2017. As it is, somebody at Cell C got themselves a phone set and upgraded my account which I do not have as it is closed as far as I am concerned and yet every month sometimes twice a month, an amount gets deducted off my account. Anything from R47 to nearly R400 gets deducted off my bank account. Who gave Cell C the permission to upgrade my account without my permission and knowledge? Who gave Cell C the permission to deduct money from my account - this is FRUAD. Who at Cell C has taken the new phone/handset which was not permitted....? My contracts are all closed - stop deducting money from my bank account. I have a pre-paid account only . . . . . . .