I had this issue with IBKR in 2003, I bought 200 shares of something that was not traded much in the premarket session that was offered in the order book, which was currently $10 below the current market price ($2000 instant winner).
They called me and broke the trade and refunded the commissions.
What's appalling is that they charged me extra commissions to reverse the trades. If it was the exchange that's f'ed up like what @rb7 said, then I shouldn't have to pay for anything when IB tried to remedy their f'ups. In my case, they didn't even call me. They just gave me a notification in TWS that my trade is suspected as an erroneous trade and they are going to investigate. And then they gave me a second notice that stated to me that upon their investigation, they deemed the executions of my trades were erroneous trades and then upon the close of business, they reversed the trades and charged me extra commissions for the reversing trades.
Ok I am going to contact them. At the least I shouldn't be paying for their action of correcting their mistake.