Loss of trade in promotion deal

I traded in 3 phones with Xfinity to get 3 brand new phones. The trade in deal was $600 per phone that would be dispersed in 24 installments of $25. In the store i asked if I could pay off what I still owed right away, and they said they couldn't without removing the promo. However they told me that I could pay it off later and that my promo deal would be fine. Several months go by until I got around to it and I had 17 payment left on my 3 phones. I payed off what I owed to each phone to lower the months cost, but instead it went down to 8 payments left.

I tried talking worh customer support but they said they can only refund the money back to my account as an overdue payment. They said this won't change my phone payments back up to the 17 payment, and I would just be paying more each month. I would not have made the extra payment if I knew it would remove my promo deal.

I then went to reddit for help which they opened a ticked with the xfinity moble team, but the representative basically said I lied and that they couldn't do anything.  They closed the ticket on me and, now the reddit people can no longer help.

I am loosing 9 months of $25 for each of the 3 phones. So is it possible for me to get a maunualy credit each month or a lump sum credit. Or is someone able to refund the money and put it back onto the phones to keep the promo activated.  There has to be someone at this company who can help get this fixed.

Thanks.