He's placing a bet across different platforms on the same game for the same result. Far as I know, what's prohibited is arbitrage betting, where the bettor placed bets for multiple outcome. Given OP placed bet for the exact same outcome, I don't think that's prohibited. Unless a clause in BC's ToS specifically prohibit this... can you perhaps point it out to us, please?
Odds providers usually limit the maximum bet amount a user can place on a market; this is a common risk management strategy implemented by every odds provider. When a user exceeds the limit placed, they're not allowed to place more on the same market, and since we share the same odds provider, the limit was enforced cross-site. The 5-day delay in voiding the bet makes it awkward, but this is what has transpired.
The odds provider is fully at fault here, not me. Most users wouldn't even know which sportsbook uses which provider. If an odds provider does not want more than a certain amount of stake on a certain game, then they should simply arrange their system in a way where odds drop after a certain total stake, or that bets are not even accepted at all anymore.
Next to that, I don't see what difference it would make if one person (me) places 2 times a stake on a certain game, or if it's 2 different persons. The risk/reward is exactly the same.