Transit Xiamen without permit?

I got a round trip ticket to Seoul with connection through Xiamen both ways, each less than 24 hrs layover. Because first layover was less than 24 hrs, no 72 hr transit permit required. But when I missed the connecting flight to Seoul, I was there over 24 hrs and fined for no permit and told I can't transit in Xiamen on the return leg, no longer eligible for free transit. Cost for legal permission to connect in Xiamen quoted over $600 now. What happened to free transit permit? This seems ridiculous.