I can't play on multiplayer, neither joining a hosted world or trying to host a world. When I try to join a game of a friend, it says that the game no longer exists, and when I try to host a game, it says that occurred a problem while trying to host a game and that I should be check my Internet connection and try again later. I've saw many solutions that it seems to work for some people but it didn't worked for me, and it not the firewall or the anti-virus.

Hi!

I'm sorry to hear that you've not been able to play Grounded with your friends. I understand how frustrating that can be. There are a couple of other things you can try. I'll post them below. 

https://support.xbox.com/en-US/help/hardware-network/connect-network/network-ports-used-xbox-live

https://support.xbox.com/en-US/help/hardware-network/connect-network/xbox-one-nat-error

If either of those solutions don't work, please feel free to submit a support ticket. There we will work with you one on one to gather information related to this issue. 

Obsidian Support

Thanks!