Jet ignores request to cancel airtime contract

I cancelled an airtime contract which was imposed on me with a service provider o don't use: Cell C. I have been trying to cancel this since April 2020 with no success but it continues to deduct on.my premuim. I dont know who is benefiting from this airtime contract. Jet is turning a deaf ear and are cutting me off once i call and mention airtimr contract.