Cancel debit order

Consider the pain of your divorce - it appears to be very hard. I have a contract which has long expired and has been inactive for over a year so, logically, I want to cancel it. On the 5th of November 2018 I called Cell C and requested to cancel the contract. I was put through the verification interrogation and was able to answer all of the questions except give them my own personal telephone number I used when I took out the contract. That was a company number and I having changed jobs twice since I could not remember it - boom, request denied - go see an agent! On the 7th of December I went to Cell C in Menlyn and requested to cancel the contract. Well, the agent does not process such requests, I had to call Cell C. So I did, using the assistant's telephone (thank you for your kindness). An extremely helpful telephone assistant tried to convince me not to cancel, but I insisted and he finally accepted the request, indicating that everything was put into place and that the ball would roll. Well, the ball rolled to the next debit order on the 31st of December and, as was to be expected, the normal amount was deducted. So now I wonder, how do I disband this (one sided) marriage? I was the only one to have signed the contract - does it mean that you, Cell C, has no obligation to honour my cancellation request? Does the contract only exist for me? Will I see another debit order deduction at the end of January 2019 and beyond? Your one and angry