I have a friend with a server, the server was in top15 gt.com, but now i have a problem, someone else have the ownership of the page and when I try to take the server back it tells me that I took it, it appears to me that it is mine, but it does not exist on gt.com, but the page does exist.

Server page: https://www.gametracker.com/server_info/87.98.130.173:27015/

How this can be possible?

Moved: Not a Gametracker bug.

If you mean this server page: https://www.gametracker.com/server_info/178.33.52.74.lvlup.host:27015/ then I am not surprised it does not exist/

You cannot concatenate an IP address to a domain name and expect a sensible result.

What is the IP address of the server you claim to own?