If you are able to access Virtualmin on port 10000 via your domain name then the domain / DNS records are setup correctly. You are able to access Usermin on port 20000 via the IP addresses so I am a bit puzzled about why the domain does not work.
Check if the vps host’s firewall has port 20000 open.
This step is necessary in case the IP address used by you is a private IP address, which the firewall might not molest.
Also see Unable to access port 10000 in web browser
I really wish people would provide real examples for domain names and ip addresses, it would make troubleshooting so much quicker.