Credit due to me, vodacom refusing to pay it

I contacted Vodacom in April 2017 and request to settle contracts which is called pre-mature cancellation. The contract was settled and cancelled, 3 months later I discovered that vodacom was continuing to debit my bank account for an account that is settled in full. I contacted them right away, they sent me form post to pillar and eventually they admitted that the error was on their side and that there was a credit due to me. I asked them to immediately stop the debit on my account and start with the process of refunding me for the credit that is due to me. I contacted them several times trying to make a follow up on my refund, again was sent to one department to another and all refusing to take ownership of the refund. I even escalated the matter to one of the team leaders whom she assured that my refund should reflect in a couple of hours.....that I am still awaiting for to date and it is now 12 months.