I would like to know how to file a complaint about a rude employee at an at&t store

My husband and I went in to our local store to acquire information in regards to an account that we had started on a prior day. We were told after speaking to several customer service reps and supervisors on this particular morning that no deposit was needed and that they could mail our phones to us for a BOGO Deal Promo or we could go into the store and get it. So we went into our local store,  we were greeted rudely, the person helping us was acting like my husband was telling him untruths, he kept saying that what we wrre saying wasnt accurate, he was mumbling under his breath to other employees about us (in front of us), he was argumentative, we got no help at all from any of the other employees or supervisors that heard what was going on. It was the worst experience that we have ever had! I cant believe that type of employee would be allowed to help other customers!