CELL C ON CREDIT REPORT

I used to have a cell c contract phones. I paid the contract and at the end of the contract I informed cell c to cancel the contract . Since then both my numbers are on prepaid. Now when I checked the credit report from transunion it stated that I still owe cell c a balance of R324 and I know that I don't owe them anything as I finished the term of the contract and cancelled it . I called their customer care where I was told that contract department need to sort it out . I spoke to the lady Rea who was very rude and didn't want to assist. When I requested a reference for the call she gave me a number , I told her to repeat it because I wanted to see if she gave me the correct reference number secretly, she then gave me a different number. When I asked her why is she giving me different reference number she rudely said she didn't. I told her that I intentionally asked her to give me the reference because I knew that the numbers are not correct. I need to close this account as I don't owe cell ce anymore. Please assist ASAP