Still no Refund nearly a month later

I made a purchase on the 21 November 2023. I followed up a few days later as I had not had any communication from this company, only to be told the lengthy wait on delivery. Still no communication and then an email to say they didn't have stock of the order I had placed on the 30 November 2023. They offered me an alternative product or refund. I sent through my details for the refund on the 01 December and have been following up since and have still not received my refund. I tried calling them this morning, but their line has an answering service saying that they don't take calls on their platform and only accept emails. So, how do I now go about getting my refund?