Did you try to go through Amazon’s online return process? It should be a case of clicking a few buttons. There is an option for “incorrect item delivered” and to choose either refund or replacement.
The obligation is for Amazon to complete the order correctly, though I expect that they may want to review it, given the high value.
Swapping of high value items is a known scam that has been reported in the press. I even recall cat food being used as the “mistaken item”.
I find the best way to deal with Amazon customer service is to use the live chat box. It’s somewhere under ‘contact us’, but not that simple to find. It’s a bit clunky because everything has to be typed in, but you get to interact with a real person and they will push it up the hierarchy if necessary. Keep pushing - they should have authorised the refund by now.
My disillusionment with Amazon is pretty much complete. Having been a victim of the bait and switch scam with a set of Bose QC Ultra earbuds ordered during the Prime promotion but which was a pack of spacers and washers I eventually got my refund. Then ordered the earbuds again at start of Black Friday promotion. The external packaging seemed fine and there was a Bose box inside. Perhaps should have twigged something amiss as no shrinkwrap but there was a tear off seal which when removed enabled me to open the box. Everything in the box….except the earbuds and dock… Return process started again but starting to feel like something very wrong with the Amazon supply chain processes.