I am not sure any attorney would be able to answer your question in a vacuum; more details are necessary as is a review of the pertinent documents. I would recommend requesting a free initial consultation.
This response is for general purposes only and does not create an attorney-client relationship.
It is very unusual for a buyer to pay the commission on a house that he or she is buying. Are you sure you were charged a commission on the home you purchased?
Review your listing agreement. This will outline what you agreed to. If you signed an agreement without reading it or without understanding it, then you screwed up. If you did not sign an agreement, then the broker may not be entitled to any commission at all.
You don't say what the sales price of your home was so it is hard to tell what the total commission was. It is typical that you would agree to a set commission and, out of that percentage, the listing agent will pay somewhere between 2.8% and 3% to the buyer's agent. All of this is laid out in a written listing agreement which you should have signed before your house was listed.
You may want to hire an attorney to review your paperwork and help you understand what you signed up for and what you were charged for.
You can reach Harkess & Salter LLC at (303) 531-5380 or info@Harkess-Salter.com. Stephen Harkess is an attorney licensed in the state and federal courts of Colorado. This answer is for general information only and does not create an attorney client relationship between Stephen Harkess or Harkess & Salter LLC and any person. You should schedule a consultation with an attorney to discuss the specifics of your legal issues.