My perseverance has paid off. I have been at the radio on and off for prolonged periods trying to work FT5ZM Amsterdam Island all day. First it was 10m SSB. No joy. Then 12m CW. No success. Then I QSY'd down to 15m SSB, where my friend Don EI6IL worked them but they faded out soon after. I then tried 17m CW, where the pile-up was 20 Khz wide!! No success there either. So finally I hit 20m CW, and long into the darkness they were still a good signal here on my hexbeam.
At long last, just eight minutes ago, I heard what sounded like my callsign coming from FT5ZM. He gave "I2KC 5NN". I replied: "DE EI2KC EI2KC 5NN BK" and he said "EI TU". Brilliant stuff. That's DXCC #303 in my log. Chuffed.
Above is a video showing the signal strength from FT5ZM immediately after I worked them.