Vodacom Debt Settlement

Vodacom is robbing me. I had an unsettled account that was over 5 years old. And was only recently contacted about paying it off through JBA debt collectors. I have been paying them in monthly instalments. I have added up the instalments I have made to them and they do not match up. The account should have been settled long ago, but they are STILL contacting me for over R2300 for settlement which is not possible. They are just making money off me by hounding me every day about an account that I had 5 years ago. I have been with cell c for 5 years, why is Vodacom still contacting me??? And after the many month's of instalments, I have made? The account is settled long ago!! This is a third party debt collection that has not provided me with any official documentation or statement or breakdown of amounts owed and paid.