Wrong chromebook was sold and now I cannot return

I need help. Who can I talk to? I went to ATT in May. Got a new phone and a chromebook on promotion. After a month, I called ATT store and asked why my chromebook promotion was not taking effect. The kid that sold it to me said it takes a few months. So the third month, I called again to discuss my bill. The manager Gary told me I should have asked questions the day I came in and I should have known everything. He later said sorry he said that but I was extremely confused why he would say that to me. I did a chat convo online with ATT recently and they told me I was sold the wrong chromebook and it did not have a promotion. I looked up the price difference. I was shipped a $800 vs $350 chromebook. After being told by the manager, I should have known to ask questions and I should have known what was going on, I feel extremely frustrated more so now. The manager did give me the promotion but instead of paying $150 I am paying $400. I called the store again today to discuss if there was anyone to help me. Seems my calls are not going through to them. Finally someone answered and didn't hang up on me. The guy on the phone would not give me his name, said he didn't have to disclose his name and said he was short staffed and helping other people and to have a nice day oh and try and return at another store which the manager told me I couldn't return. I just want this chromebook out of my life but I cannot find anyone to help me. Any suggestions?