They responded to my ticket and said that I had insufficient founds on my USD card to cover the monthly fee.
That's weird. Mine's been kept empty for months on end and they haven't said anything. I stick some money on there and disappear again. I assumed if you keep it empty the fees back up until it's loaded again. Seems onerous to keep freezing and reopening.
I had it empty for about 6 months before they closed it without a warning.