Vodacom Complaint

I am very upset with Vodacom as my contract with them was about to end they called and offered an upgrade and I declined the offer and asked to pay until the end of the contract which I did pay at the end of the contract on December 2024. I am now receiving an email from them stating that I will be paying in January 2025 while contract ended December 2024, I even wrote two emails to them telling them that I am canceling the contract after I'm done paying the amount that is due. Please help me because I can't keep paying Vodacom for something that im done paying for.