Traded in iPhone 8 plus for promo credit. 7 months later, still no credit

So I've basically just accepted the fact that att straight up stole my ohone at this point. I traded in an iPhone 8 plus for a promotional 300 in bill credit toward a new galaxy s10. After 3 months I started calling customer support to ask where the credit was and was told every time that it should show up. 2 more months go by when I call yet again. This time it was discovered that for whatever reason, the company that handles trade ins and the billing department didn't communicate and my credit wasn't processed properly. I was assured it would be handled. 2 more months later and I'm still getting the run around. I getting told they'd escalate the matter and that i would get a call within 72 hours. Never get a call. This company is (Edited per community guidelines)ing bogus. At this point what am I supposed to do? (Edited per community guidelines) up? Contact BBB? I'm at a loss.