Refund never recieved and now given extra Charges.

I purchased the samsung21 ultra online and recieved a box with only a charger in it. Called at&t they kept telling me if I report it missing I can't use it. That's not a problem because I don't have it. They claim to have canceled the trade in too. The purchase was 11/12/2022. I have called several times to find my case has been closed. As everyone knows you're charged tax before you get anything even if you're trading in. Even though my bank shows I was charged, still no refund as of 2/11/2023. I've called once a week since this occurred and still no help. I contacted my bank and they claim at&t states I was correctly charged even though they claim I was not charged to begin with. In addition I recieved a text saying they're billing me for the remaining installments on my phone that I was trading in with the next up plan.