Question Vodacom Business ethics

On 20 May 2022 I cancelled a data contract that expired on 29 April 2022. I was told that I must give 1 month notice which I accepted. So contract was cancelled 30 June 2022 with last payment. The agent told me no need to phone again it will be cancelled at the end of June. I was surprised to receive an invoice at end of June 2022 relating to this cancelled contract for R10.94. When I enquired I was told it was because I did not phone the day before contract was cancelled to confirm! I was not going to accept this and was transferred to ‘cancel contacts’ dept. I held on for 15 minutes with no reply! This is unacceptable and I am sure a nice income for Vodacom. It they do this to 1000 other customers that is an income of R10,000. Sure there is more than 1000 customers with same experience. I question Vodacom’s business ethics. Will never deal with them again! Their customer service is also nonexistent.