Canceled contract

I have an MTN contract and I started receiving emails as well as sms messages informing me that my contract is up for renewal. On 14 November 2020 I emailed MTN informing them I do not want the contract renewed and if they can convert the Sim card to pre paid. I received no response but they continued deducting the debit order. On the 9th March 2021 I sent another email informing them of the same. I have now received an email from them informing me when the next debit order is going off. I already only use this sum as pre paid and they can go into the account to view. I want all my money back that has been taken off my bank from December 2020 and I want this Sim to be converted to prepaid. Thank you