Cell C contract cancellation

I have received a very bad experience with cell c 's retentions call center. I called them as i wanted to cancel the contract that i have with them and they keep telling me that i failed the security questions.. how can i not know my id number and my name and surname as well as my home address? and why would i want to cancel a contract that does not belong to me? now the number that i want to cancel is " permanently deactivated" now i must struggling by calling and being transferred from one department to another.. i'm so ****ed. can anyone from cell c contact me and fix this mess because this whole thing is gonna affect my credit profile