MERKADO accepts payment but fails to produce sold item in 3months time

I made an order more than 3months ago on Merkado internet sales. I paid more than R1040. 31st May I got an email from them stating " order has been delayed and will not be dispatched until the week of xx ***x." Of course I enquired what the expected date of delivery would be and rcvd the following response "We have passed this query to the relavant team who is looking into the ETA ". Since then I have neither received the product nor any further communication from them. 4days ago I asked for a refund, no reply received to date. Any advice on the best legal route to prosecute?