The transaction was at 8.85. Is it possible you entered 8.85 vs 18.85, and did not see the "1" was missing? You need to find out the bid at the time stamp you entered the order.
Read your brokerage agreement. Yes you can always bring litigation, but you may have already agreed to an alternative remedy. BTW this is why you should also be 100% truthful on your new account form. It will be defendant's exhibit 1.
@gate, Do you live in Montreal or have any contacts at the brokerage? They are about a 5-minute walk from where I used to live in Montreal. If you are close, maybe you should just go over there and talk to someone in person. People often act completely different when you talk to them face to face. But if you entered the order at the wrong price like Robert Morse said, you are probably screwed.
I modified a cancelled order at $18.85. I did not even touch the box of the price. I just changed the quantity and checked the box for after hours trading. And checked 3 times to be sure that everything was fine. The bid on ARCA was only $6.40. But on my broker website I was seeing 4300 shares on the bid side. I want to know on which platform it was. It would certainly help my case.