You cannot connect directly to ipv4 server (which Tibiantis is) from stricte ipv6 network because both protocols are different. In this case you should use transit proxy service (should be done on your ISP side) like 6to4 (deprechated), NAT64 or DNS64. Most of VPN's also have such feature built-in.

Here is a free nat64 I found: https://nat64.net/
I believe that setting it up in your system will resolve this issue