Order cancelled but no refund received

I placed an order with Adidas Online and they confirmed my order. When they had to deliver they told me that the item I ordered is out of stock so they will be cancelling my order, that was 3 months ago and to this day I still haven't received my refund. Everytime I call the head office I'm told that I will receive a refund after 5 working working days but I still haven't received it 3 months later.