Struggling to get refund from Argos

I ordered a new washing machine on 2nd November, however due to issues with installation I cancelled the order on 12th November before it arrived. I paid with my Argos card and was told the refund would be processed and back on my card within 7 working days. On 21st November I contacted them again to say refund has not been received, I was told that "The order has not been updated, I will get this actioned for you immediately and the refund put back on your card". I was told this would take 3-5 working days! I have both transcripts for these conversations as they were done via live chat. On 27th November I called them as the refund had not appeared still. I was told once again that it had not been processed and they were going to sort this out right away and speak to the "Back Office" and it should again take 3-5 working days to process. I was fuming by this point. It is now coming up to the 5th working day and I have still not received the refund. My question is: If this refund is still not back in my account by tomorrow, what next step can I do? I have been told 3 times it has not been processed and I have still not had my money back! Help!