Ask them instead of busting the trade, to reprice it to the best bid at the time, or at least to the mid-price at the time of the trade. I.e. you still get your fill (albeit at a slightly less favourable price) rather than being left short the put. If they refuse then I would make very loud noises about lawsuits and negative publicity. Try contacting a few media outlets and get them to take up the case.
Trades should *never* be busted IMO, at the very most they should be repriced to "fair pricing" at the time of the trade.
Trades should *never* be busted IMO, at the very most they should be repriced to "fair pricing" at the time of the trade.