I've been gambling for decades, and if it's a normal thing for books to cancel bets when they don't go their way, than I'm very uninformed.
What happened: Betfury has cancelled open bets that would win ~$400k. They have refunded the value of the initial bets which was ~$100k. Therefore I feel I'm being owed another ~$300k.
The risk department has deemed my sportsbook play as high risk and at that point they canceled a bunch of open multiple bets, most of which already had one or more winners (see images of the bets below). Those bets would go on to win over $400k had they not been canceled. Betfury has only refunded the initial bets which amounted to just over $100k. They offered to compensate me with an additional $100k bonus, but I refused.
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So you turned down 100k profit correct?
They took $300k of my profit and offered a $100k bonus as compensation. I didn't inquire about the terms. Yes, I turned it down.
What happened: Betfury has cancelled open bets that would win ~$400k. They have refunded the value of the initial bets which was ~$100k. Therefore I feel I'm being owed another ~$300k.
The risk department has deemed my sportsbook play as high risk and at that point they canceled a bunch of open multiple bets, most of which already had one or more winners (see images of the bets below). Those bets would go on to win over $400k had they not been canceled. Betfury has only refunded the initial bets which amounted to just over $100k. They offered to compensate me with an additional $100k bonus, but I refused.
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So you turned down 100k profit correct?
It's not profit. Its a compensation. It’s like the 100K means nothing to OP, just to reject the $100,000 compensation offer. But knowing that Betfury made that move (the compensation offer), it gives the impression that something went wrong on betfury end since they’re offering compensation.
If I were in OP’s position and I knew I was on the right side, I would also reject that $100,000 compensation offer too. But if I knew that the sportsbook’s rules allow them to cancel open bets and void combos, then I guess OP should consider accepting that compensation offer.
Obviously I didn't know they were gonna cancel the bets. If I did I wouldn't play there. No one would. That's the whole point of this thread, to disclose their practices to the public so they either redeem themselves by fixing the issue or take a reputational hit. No one is going to play at such a book.
The legality of it is a different matter, that might come into play if we get to court.
I think the least Betfury should offer you is the total of all cashout amounts added up.
That still is not nice behaviour because a cash out often is a way too low amount, but at least it's fairer than what they did now.
Yes, I even offered that as a gesture of goodwill from my end, they refused.
Just to be clear, the games finished?
Yes.
Let's say other player placed same bets, they'll win as there is no ruling or event or anything that'll officially void the matches?
Correct.
Only your bets got exclusively voided, manually, by BetFury? Do they also give an explanation why they manually cancel the bets? I peeked at their ToS and I do find an extensive explanation that cover their right to void bets, such as, but not limited to, as below:
Yes.
Do they also give an explanation why they manually cancel the bets?
They say they can cancel any user bet.
I peeked at their ToS and I do find an extensive explanation that cover their right to void bets, such as, but not limited to, as below:
That is their primary claim, they can cancel any user bet, end of story. They also make some wild claims that "in my case, the events weren't finished". These are purely false. Events either finished or did not, there is no "my case" or anyone else's. And in this case, all the events finished normally.

Hmm... I'd like to contend this ruling they made with "the bets technically finished. It got unfinished just because you cancelled it. Otherwise, it'll be finished."
They're with Betby, though, and I guess it's one of their yet another mischief. They've been stirring some problems across casinos with questionable rulings and decisions for the past couple of weeks.
Nonetheless, let me try to nudge them here and try to get their side heard.
Thanks, I appreciate it!