Terrible service...

Terrible service. Quick to take your money but no customer service. When you buy online, usually when sizes are taken it is no longer available to order. But my money was good enough to take till I followed up on my order 10 days after paying for it. Only to find out that those shoes I ordered was out of stock. Then I distinctly asked for a refund, which I am still waiting for... After handing them my banking details a week ago. Pathetic. What am I to do to pursue them?