Still being charged for contract after cancelling in April 2022.

I cancelled my MTN contract on the 05/04/2022 and received an email on the 05/05/2022 stating that my contract is no longer a contract but downgraded to prepaid. I received an invoice today 11/07/2022 stating that I owe R176.00. I called MTN Liyanda transferred me to the retentions department who I spoke to Nikita who confirmed that there is nothing owing and then she transferred me to the billing department who I spoke to Anele who could not even get my ID number right and eventually cut the call. I want this issue sorted out with immediate effect!!