Cell c wants me to pay R500 for a contract I paid in full,after 5 years 2 contracts paid in full .

I had a 24 month contract with cell c which I paid in full even though the phone is ******, after paid for 4 months on a month-to-month just for the data when I lost my job I called cell c to cancel I paid them in full and they still gave me a bill of R500 ,when you call the call center they can't assist and now I have to pay R500 for a contract that I paid in full because if I don't il be black listed and I'm currently not working.

I truly regret referring my friends and family to cell c I will not even use their number as a prepaid SIM card they are the worst totally unacceptable behaviour and treatment