I recently had a recliner reupholstered and asked for the old seat cushion to be used. It was molded to me and I didn't want to start over, so yes, some people want the old cushions used.
However, if you told them you wanted new cushions, you should get them, no matter what. And without further cost. Was there a witness to the conversation? If so, remind the company that you aren't the only one that heard that you'd get new cushions.