Struggle to cancel a contract not in use anymore

I've been with Vodacom for 27+ years. I want to cancel a data contract and after various calls the contract is still not cancelled. Every time I phone after the so called cancellation, I find out it still wasn't cancelled. I am not interested in ANY DEALS! I work for a fibre company and do not need the data anymore. Please cancel the contract, I haven't had any problems until now.