This rule obviously impacts the betting markets since the game can never go into overtime since the game will only finish once a team hits the decided target score within the game. For example if you were to bet on draw you would never be able to win in theory.
More importantly, is it possible to bet on a draw at all?
Also, you took the overtime option there in your bet, so you bet on the final end score, and you lost, I don't see any reason for that bet to be returned, even ignoring your claims about now knowing what the rules don't really count.
OP needs to be familiar with the rules as bookies doesn't really review the odds and market they provide, they have the odds provider and everything was link in their. If that particular game has no possible OT outcome but the OT market is available in the sportsbook for betting, then that is quite misleading at all, but that's how the game work I guess, and we will never be mislead if we are familiar with the rules of the game and the certain league we are betting.
however, it's still good to see a reply from blackjack.fun about this since they are active in the forum, but I don't expect the bet to be refunded IMO.