Lost order not being refunded

I placed an online order on 28 November 2020 with a delivery estimate of 5-10 working days. Order no: ***. On 01/12/20 I received a notification that the order is ready to be shipped. On tracking the parcel I also noted that the parcel was received by the courier company on 01/12/20 for delivery. On 07/12/2020 I checked the tracking again and noticed that it still stated that the package was received on 01/12/2020 and would be dispatched. That means it was still with the courier company for a week with no further activity. I contacted the call centre who advised that the package was lost by the courier company and that I would need to request a refund - which I did. They advised me that they would escalate this to the refunds department who would contact me within 24hrs. Complaint number: ***. Nobody contacted me as promised so I called the call centre again on 08/12/2020 at 11:13. They told me that the matter has been escalated and that the refund department would contact me within 24hrs. Once again nobody contacted me and I called again on 09 December 2020 at 16:58 and was again told that the matter has been escalated and that they would contact me. Again nobody contacted me so I contact the call centre again on 09/12/2020 at 12:48 and was again told that they would contact me. Once again there was no response and I called the call centre again on 14/12/2020 and was told (once again) that the matter would be escalated. I now have no other choice but to approach their legal department with a letter of demand for the refund as they clearly have no intention of resolving this matter.