Customer opened an A-to-Z claim because his order was running a few days late (carrier delayed)

I had previously sent messages to the customer offering to send him a pre-paid return label and pick up in front of the house once the item was received, which he ignored.

He opened the A-to-Z claim, obtained his refund before the item was refunded and a few days later still accepted the delivery of the item. While I had requested RTS with the carrier, it didn't work.

I wrote the customer a message to take back the item. Is Amazon agreeing with the customer keeping the item despite being refunded or is this pure fraud?

In this case, would I get in trouble if our lawyer sending a legal letter, given that the customer does not cooperate sending back the item with our pre-paid label?

Thank you