$400 Device Credit Not Applied

I switched to Xfinity Mobile in September 2025 under a promotion that included a $400 device credit on an iPhones. This was the promotion as I got new Xfinity internet connection with 1GB data plan. I added two lines and purchased IPhone 16 Pro and IPhone 16e. But, I observed that bills doesnot reflet any device credit. I have been paying my bills as if the offer never existed. I would be glad if this problem is resoloved here.