How to escalate issue to upper management for Trade In promotion ?

I agreed.  Don't believe that they will honor their promise.  I received a notice for a free phone upgrade when they had the 3G Network shutdown.  I had 4 phones to upgrade. I called in at different times. Each time a new promotion ran.  After negotiating with the Customer Service, I got all the phone upgraded. However, I had to call in every month to get the reimbursement ($28.84) for two years (started about 8/31/2022). Now, they are telling me that I can't get the reimbursement because they have no documentation about the 3G Network shutdown promotion.  I am now stuck paying the remaining charges.  

We need federal laws to allow consumers to get corporation's customer service notes when they promise their customers discounts and reimbursements. I