He said he posted it, but it didn't arrive, so I agreed that he could try posting it again; after several days with no confirmation of posting I asked for the refund, which he agreed to.
He said it had been returned to him and gave me a screendump of the delivery proof; on looking at the tracking number (PN518894078GB), the track & trace info only shows it being in the Midlands (I'm in Berkshire).
He's now threatened me with legal action for slander and I've responded that if he points out anything I have written which is untrue, I will be happy to withdraw or correct it.