Order Cancelled No Refund After 4 Months

Purchased a vacuum cleaner online. They took two months to respond by which time I had called to cancel the order. In the meanwhile I had obtained the same item from another supplier. After 2 months they send the item. I sent it back. I called three times, went to their Willowbridge branch, emailed. Still no refund. What must I do to get my money refunded?? This is theft! Please refund me