What are my rights with Argos

Hi, im not sure this is the right bit to post but couldnt find any other place it would be relevant. 2 Months ago we ordered sofas from Argos in the sale, a large leather sofa and recliner chair for around £483 in the sale. We were expecting delivery within 28 days as stated in the catalogue. The first date i was expecting a call by, they never phoned, i called them, they said i will next be contacted by 2nd Aug, a month after i had already waited a month as they were having trouble getting the large sofa from the suppliers. 2nd Aug cam and still no phone call, i had to phone again and they said the sofa is still delayed and i would be contacted by the 16th Aug. They have just phoned saying they cannot deliver them as they are now out of stock! I have been waiting just over 2 months for these, its our first flat so we havent had sofas for 2 months, they offered me a refund or 20% off ordering other sofas. If i ordered sofas similar to the ones we wanted with the 20% off we would have to pay an extra £200! What are my rights? should they supply me with the next best thing similar to the sofas i ordered at no extra cost? I am just so angry as we have been sitting on the floor for the last 2 months! Hope someone can help, thanks Emma