Cash refund on item bought

I made a purchase on 24/11/2018 and my order was canceled due to supplier not having stock available. Superbalist.com then credited me a voucher which i did not ask for as i paid from my back account. I called them requesting they return my funds they took my credit away and ensured i will get my money within 24 hours it has been a week and they still have not refunded me, I've been calling for a week with calls reaching a time of nearly 30 minutes daily for the week passed. They are now costing me more money just too get my R366 back. Everyday they are coming up with more and more poor excuses. Totally disgusted and unsatisfied with their service.