Vodacom Cancellation and Refund

I've been calling in at least twice a month since 4 Jan to cancel my contract with Vodacom since it expired. However, I am still getting invoices re: data and voice. The assistants claim that my account is on the old system which they do not have access to and need to escalate for the cancellation to take effect. I was told I would be contacted regarding a refund and up to date, I have not received such a call.