Not receiving promised promotional rate

I am having trouble receiving the promotional rate I was promised.

I spoke with customer service on September 9, 2025, and they enrolled me in the xfinity mobile promotion of $20 total for our two lines of unlimited, for one full year, with confirmation [Edited: "Personal Information"]. However, I kept getting billed at the original, higher rate.

I spoke with customer service agent named Vishal on November 28, and he confirmed I should be getting an xfinity mobile rate of $20 total for two unlimited lines for one year. He processed a one-time refund of $40 for November, but I continue to be overcharged by $40 each month, and no corrections were made going back. I can’t keep making this request every month. Can you help, or somehow compensate me one time for the $480 total savings I should accrue over the year? Thanks!