DNS cannot be accessed

Hello! I’m from China. Recently, I’ve been experiencing issues with NextDNS where web pages fail to load, but switching to other DNS services resolves the problem. This issue is not limited to websites, some apps also show "no network connection." I’ve noticed that the Hong Kong server, which is usually connected from mainland China, is not working, and the Seoul, Tokyo, and Taipei servers show time, but take nearly 20 seconds to load a web page.

Is it because the Hong Kong server no longer exists, or has it been blocked by the Great Firewall? If so, can I request a refund? Thank you!