It's almost impossible to say for sure that a betting website is totally fair or not unless they're being really obvious in cheating, it's usually in the way that if you win a lot you'd think the website and their system is totally legit and if you lose you would think the system is rigged and not fair, but in this case if you have a proof of them canceling the winning bets just make a thread about them in scam accusation section with all the proofs if you haven't already so that others don't fall in the same trap in the future.