Add a line free phone

I added a line to my family plan in May 2022. The promotion was I would get a free phone. I called today regarding a different issue, and the customer service rep is looking at all my devices, to my surprise. He says I have been paying for that phone since May 2022 and have not been receiving a credit. He spent over 2 and 1/2 hours researching it and concluded he can not adjust what I have paid to date, nor can he adjust what I still owe. Apparently, the rep who added my line did not use the promotion. 

All of my lines on my family plans are a mess regarding devices. Kevin in customer care agreed something was done incorrectly, and I have been paying on devices I should not have or are on the wrong lines. But there's no help to fix any issue. 


What can I do? Can I file a complaint or outside help?