Unfairly treated by Vodacom

Unfairly treated by Vodacom, I had a contract with Vodacom which expired end of Feb 2021 and I cancelled the contract on the 12.04.2021 around 08:00 in the morning. The reference number was given ***. My number the following month was then converted to prepaid and the debit order was also cancel. I was surprise then last week when I get a call from Vodacom telling me that I owe them 158.00 and my contract is still active. I total disagree and I need that amount cleared and my contract cancelled as per my previous request. This is one of the other reasons that made me not to renew my contract with Vodacom the treatment they are giving to their customers it's very bad. They are now affecting me negatively to my ITC record. I also need an explanation and an apology why my contract was not cancelled at the time when I asked them to.