Unacceptable service from AT&T for so called "guaranteed "promotion

I am completely outraged at ATT for falsely advertising a "guaranteed" promotion (free with qualified trade in) on 2 Samsung S24 phones that I added to my account, one upgrade and one brought from Xfinity. I followed all the rules, purchased a used S8 phone online because my S7 was not included in the trade in offer to get one phone, and completed the purchased online at Best Buy in February. I finished all the steps and assumed it worked because Best Buy emailed me their added promo of $150 gift card per line. But the software between Best Buy and AT&T did not give me the promos and they are making me, disabled on low monthly income and my 85 year old mother pay for both phones. I spoke to customer service and supervisors day and night and they are making us pay full price. It's ridiculous,  why would I want to pay full price when clearly every company out there is running this promo? Because for some reason I don't understand, I didn't get the promo and no one over the past 4 months could explain why, they tell me it is to late to return. I don't want to return, I only want to send in the phones and get the promotions that are "guaranteed". This is below any bad service I have every received from a professional company.  I am considering going to the news and possibly small claims court, in the least take my many years of loyal service anywhere but AT&T because clearly you don't understand what customer service actually means!