MTN is harassing me although I have paid up and canceled my contract in August 2024

MTN is harassing me although I have paid up and canceled my contract in August 2024. Today I received a message from MTN saying I owe them R385, and in December they were unsuccessful to deduct. I have sent them messages since 2024 of which they acknowledged that I have paid up they said the bill is from their insurance of which I also disputed. MTN must be professional and the reviews is not good for such a big company. I regret taking a contract with MTN and I will never recommend even my enemy there.