Non Delivery and and refusal to replace the non delivered (out of stock) item with another one of the same value

On 25 November 2022, on Black Friday, I bought and paid two compression tights that were on 50% off discount online. I bought one WOMENS AERO REFLECT HI-RISE COMPRESSION TIGHTS - SOFT FOCUS/PEACH WHIP REFLECTIVE / L, original price 1999.00 and paid 999.00 on black Friday. I also bought one WOMENS MOTION PRINT HI-RISE COMPRESSION TIGHTS - FOREVER SPACEDYE/WHITE / L, original price 1499.00 and paid 749.00 on black Friday. 2XU state on their website that they deliver within 2 to 5 days. On the same day (25th November, I received the e-mail that they will let me know as soon as my order is ship. On the 2nd December realising that I haven't received the e-mail about shipment of my order, I wrote an email to enquire about the status of my order. On December 4th, Alvina their customer service agent responded and said she had requested urgent feedback from the relevant people. On December 5th, Alvina updates me and said my order was in a picked status and should be dispatched within the next day or two days. On December 8 I received the order but is was only one item in the package, the item that I paid 749.00 for. On that same day I then wrote the e-mail to inform the 2XU that I only received one item. On 9th December Alvina responded and said "We are sorry to tell you that we have not been able to source one or more of your products in your latest order. Womens Aero Reflect Hi-Rise Compression Tights Soft Focus/Peach Whip Reflective / L Please let me know if you would like us to replace the item with an alternative or if you would prefer a refund.We sincerely apologise for any inconvenience caused. " I checked their website and realised that the item I bought is still there, but my preferred size is sold out. I then look for a replace item with same value with the one I initially bought and paid for which is Type: Womens Aero Sculpt HI-Rise Compression Tights Product Code: WA6682B-MUL/PWF-S (Size -Large) for 1999.00 Alvina responded to say that I paid 999.00 so I cannot replace with the item which is 1999.00. Indicated that I bought and paid an item with a value of 1999.00 on 25 November 2022. They fail to deliver my item between 2 to 5 days as promised on their website until I made an enquiry, they also failed to inform me when the item I ordered was sold out, I had to wait until I receive my delivery to learn that there was only one item shipped. My argument is that yes the item is no longer on special and neither is the replacement item I am asking for, but is their fault that they partially fulfill my order, I assume the item (my size) was sold out because my order was not dispatched on time. The essence of this whole thing is that I ordered and paid during Black Friday, they delayed the dispatching of my order, and I should not be punished for their error. They should allow me to replace the item I ordered with another one of the same value. They cannot say that I need to top-up if I need an item of the value1999.00.