Unhappy vodacom customer

I did a premature cancelation on one of my vodacom contracts in February of 2019. I have sent through proof of payment and all necessary documentation to numerous people but no one seems to want to help me. Yesterday I got an email stating that I need to pay my account or I will be blacklisted. I do not owe vodacom any money. I have tried calling their customer care line on numerous occasions but no one seems to help me. They keep saying to me I need to talk to the next person. Even though I have paid in full for my contract to me canceled. The last person I spoke to told me my line is still active. Which I do not understand. I paid for it in full. But vodacom is still charging me for it. Please can someone help me for I get blacklisted for something that isn't even my fault.