My neighbour (we are not UK based) purchased for her brother (UK based) a mattress topper (under £100 value) to ship from Amazon UK.
The next day her brother (recently out of hospital from back surgery) received his Amazon delivery of a very expensive Queen sized MATTRESS (but no mattress topper). The Amazon delivery people kindly left it in his hallway and vanished while he was still scratching his head wondering what the hell???
He called his sister to find out what was going on. She then attempted for over an hour to make some sense out of the customer support bot and then after several vinos got onto live chat.
The Amazon solution.
Just keep it, (an FBA picking error, it was barcoded correctly, I asked him to check) and refunded her purchase in full. What she really wanted was for Amazon to collect the mattress and send her brother what she had ordered.
Her brother eventually managed to rehome the mattress which Amazon refused to collect. He had no need for it having recently purchased one.
In summary, she found Amazon customer service appalling bad, the steps she needed to take to speak to an actual human way too many and the solution they gave her was not what she wanted.
The stock came out of the third party sellers inventory and the refund out of their funds. I am sure they will be eventually reimbursed a percentage of the true cost.
She has cancelled her Prime account and will no longer shop on Amazon
Her brother is still waiting for his mattress topper.