This is how I block VPNs for game servers: https://zolk3ri.name/cgit/schachtmeister2/about/. It could work for any servers. It is very easy to do so. It gives you a "score" of the IP address (README.md explains it) that connected to your server, and you can decide what to do based on that, for example in my game servers there are certain thresholds. It has been working great.