Waiting over a year for my refund

I have phoned you so many times and someone will always phone me back but nobody ever does. I cancelled my contract last year in July. You told me that my phone will go on pay as you go on the 1st of Aug 2016. The number was ported to MTN mid Aug 2016, BUT you are still charging me every month. After the debit orders stopped eventually I still have not received a my refund or even just a call back from you. I got a mial back from you stating that you have requested my refind on the 17/5/2017, but still nothing. I need my monies refunded to me. This is not acceptable. I used to be a very big advocate for Vodacom, I never thought that I would be treated like this.