Vodacom refuses to cancel contract

My contract was due to expire on the 28th of December 2019, I called the and cancelled on the 3rd of December , contract is still not cancelled even now, I enquired about this early January and was assured it would be cancelled and the January debit would be refunded as the agent I spoke with in December did not cancel the contract however there will be an investigation, should it be found that I indeed cancelled I would be refunded. This has not happened .