My order has been messed up four times and counting...

Long post, but it's been a long week...

On Tuesday, I placed an order online using the current promotion on iPhone XS (buy one get one $700 off). It went through with no issues. On Wednesday, I got an e-mail stating that my order was cancelled as they could not verify my identity, and to go to a store with ID to verify. When I called customer service, they told me they could not provide any more information and I had to go to a store. Unfortunately, I'm in Canada for work this month, but I drove two hours to NY to get to an AT&T store. I explained what happened and placed the order again on Thursday. It seemed to go through with no issues. I got an e-mail saying to log onto my account and verify the order. When I did, it only had the previously cancelled order listed, nothing about the in store order. I called customer service, and they recommended I call the store. The store said they had no idea why customer service would do that, but they checked whatever records they have and they said nothing was coming up. I called customer service and the guy told me no problem, he'd be able to help. We got to the end of the order and the confirmation was sent showing two different orders for some reason and one as an XS Max... not what I asked for. He assured me that it would be fine, the $700 promotion would be honored, and after some back and forth he told me that they would give me a $10/month credit for $10 months to refund the XS Max difference, which I agreed to. I asked him to send me a confirmation message about the promotion and the credit so that I could have evidence if it became a problem later. He sent me a message only regarding about the $10/month credit. I asked for the other and he said that he didn't know what I was talking about, the only deal he's aware of is for a free iphone 8, etc etc even though we had explicitly discussed it several times. At this point, I've been on the phone for about 2 hours, so I asked to speak to a manager. He told me that they would rescind the offer to reimburse the difference (for their mistake?) if I did, but I was far more concerned about getting the $700 credit. At this point, I was on hold being "transferred" to a manager for about 10 minutes before they hung up.

When I call back, I'm back at square one. No one has an idea what's going on. Who can I talk to to solve this? There have been so many errors that I don't have any idea how much I'm going to owe and what I'm getting.