Scottrade Stop order service is Disappointing.

Few weeks ago, I started to get interested in HomeBuilder Stock (XHB). I place a stop order to buy the stock if it hit my preset price at 20 dollar. At that time, the stock was around 17 dollar. I put a order "good until cancel" Few days ago, the stock climb and finally it hit above my stop order. I was away from the computer in the whole day so I didn't check until late evening. Then, I found out my order is not executed! I was pretty upset because the closing price was already above 21 dollar, 1 dollar above my stop price. I was confused why my order is not executed. Next morning, I phone the branch and talk with the "broker" and ask for what happend. The guy give me some non-sense answer. I know the person I was talking to is new and don't even know very well what a stop order means. I then asked to talk to the branch manger. He put me on hold and he phone the market maker company and try to find out the reason why my order is not executed. After waiting, waiting and waiting, finally, he told me there was a "error" from the market maker yesterday and my order is not exeucted. To compenstate, they will buy the shares for me at $20.50. I then ask how you come up with $20.50, and he said that's the best they could do! Dudh! I was not very happy because I know if the stop order is executed right at the time when ASK above my stop price, it will become a market order And my price would be near 20 dollar. I have no way to track what price I could have got, so I couldn't do much but accept the price. I always thought Scottrade is a national brand with "exceptional customer servie", and they don't screw customers. Obviously, I was wrong and I have to consider switch to other reliable investment broker for future trades.