My Coworker Took Credit For My Sale

I recently worked really hard to develop a customer relationship with a big client, and recently my boss moved me to another responsibility (from Sales to Quality) because I was qualified to handle the multiple quality requests coming in.

Now, the junior sales person who replaced me got to "close" the sale I all but closed. Now, I have Zero commission from that sale. With the economy being tough now, I don't think it is fair for me to "save the company" by doing what is right, while the new guy gets the fruits of my efforts