Missing device promo credits

I recently set up a new line in our Xfinity Mobile account and bought a new phone that came with promo device credits. The credits showed up on the first 2 billing cycles and then dropped off. I have spent hours on the phone as well as 2 trips to the Xfinity store. I have been told numerous times that the credits were being added back but after over a month, they are still not back on the account and 2 billing cycles have passed with no credits. I am not sure where to go at this point since chatting with support, talking with support and multiple trips to the store have not solved the problem. Any guidance would be appreciated.