Amazon/Retailer/bank all refusing to take responsibility for missing money. UK

In 2022, I purchased a GPU for approx £880 from a company operating on Amazon marketplace.

This device comes from factory with a 3 year warrantee, which expires in April.

The device failed in November, and was sent to the retailer to confirm this.

Retailer confirmed it was dead, and “authorised a refund through Amazon.”

However. Amazon are claiming that they cannot facilitate refunds beyond 2 years, so they are not able to support this, and the retailer is claiming they have already sent the money.

I was advised by Amazon to take a “proof of transaction” from the retailer to my bank, and have them chase it - however my bank has said because it is longer than 6 months, they cannot charge back, and cannot compel the seller to complete a bank transfer.

To this end, I spend an entire day rotating between call centres attempting to get any clarification on this, everyone I’ve spoken to claims it is another parties responsibility to return this money to me.

Any advice on where to go from here would be welcome. £880 won’t financially ruin me, but it’s a substantial sum, and the fact I’ve been left without either a functioning GPU, or any compensation seems absurd.