Mirroring websites is extremely easy - is this all being done from one IP?
If it is either:
1. Drop the IP from your server using IPTables or
2. Block / Redirect using htaccess
#1 will mean less resources are being used on your web server as the IP is dumped, #2 will let the other server connect, try to do what it wants and then you redirect it (although with #2 you could have a lot of fun!)
You mention a IPv6 tunnel - does this mean its connecting to IPv6 on your server? If it is, and you are not using IPv6, then disable it on your server (if you can, not sure what setup you have - shared, VPS, something else)
Have fun!