Builders is a ****

Builders is refusing to refund my money after I paid for items online that were out of stock - almost a month later and I still don't have my money. When I call to enquire I'm told that I will receive an email with feedback bit nothing when I called and asked for a manager, the manager arrogantly told me that I must wait for my money even though it's frustrating because that is all she can do... I am at my wits end, how do I get my money back?