Promotional Credit not applied

I have been going back and forth between ATT trade in and Customer care for the past four months.  I traded my old phone and was sent in to the wrong facility. Contacted them and was given a case to forward my trade in phone to the correct facility in Tennessee. After few months, I again contacted both to give me update as to why the credits haven't been applied to my billing. I was told and guaranteed that I should see the changes in my billing on the first week of June. Contacted them just now, and I was told that I'm not qualified to get the credits due to my plan is not Unlimited. Told the person I spoke to that, this is news to me and that there was never a time during my contacts did they mentioned this.  The lady (from ATT Loyalty Award?) I spoke to recommended to create another case for me but would require me to update my plan but there's a catch:  she cannot guarantee that ATT will accept this term. I asked the lady that what's the point of upgrading my plan the case if there's no certainties at all.  I ask if I could just get a credit for the old phone itself,  she tried to get answers from ATT trade in but did not get clarity about this option.  I asked to create a case to get at least something for the old's phone' value... she said again that there's no assurance that they will fulfill this request.  Since I have no other option, I agreed to take the chance....

Now, I don't know what else to expect from ATT, I felt that I didn't get help at all and left in limbo.. Not a happy camper.

Any ideas where else I should be contacting to get assistance?