Terrible and Woeful service

In Dec 2015, I placed an order with this retailer for a laptop memory modules at a cost of R1,478.01. A week later, an entirely different brand and serial number was delivered to me! I emailed them on the wrong product delivered and requested for rectification, but got no response from them. Several follow-up emails was sent to them between 22nd Dec 15 and 3rd Jan16, asking for return of the wrong product delivered and cancellation of the order with full refund of my money, but still I got no response. By 2nd week of Jan, I finally got a response from a sales consultant by name Hendry, who apologised for the error in delivering the wrong product. He assured me they were going to send a courier person to pick up the product and will cancel my order with full refund. The product was finally collected by the courier in the last week of Jan 2016, in same packaging it was delivered. However, this vendor has refused to refund my money and they have been making false & baseless claim that the product was not returned to them in the same packaging they delivered it, and they cant refund my money. It's already 3rd week of Feb 2016 and they still havent refunded me. I am planning to sue them