UKNOWN won the GoT bet?
Bran should be winner as he's ruling Westeros.
but the throne got destroyed

Who will win the Iron Throne and rule Westeros at the end of Game of Thrones Season 8?
In our opinion, you can make valid arguments that both Bran Stark and Unknown are the outcomes. We plan to share the prize pool equally to those bets.
Who will win the Iron Throne and rule Westeros at the end of Game of Thrones Season 8?
Bran is ruling Westeros, he wouldn't be able to sit on the Iron Throne anyway. He's ruling from his Iron Wheelchair. He could also try to sit on the melted Iron goo. It's still the same title.
All other bookmakers list him as the winner.
By your logic you might as well pay 1/7th to people who bet on Sansa.