No Security/Software Updates - Samsung Galaxy s21 Ultra

Hi,

I switched my Samsung Galaxy s21 Ultra from ATT to Xfinity. Before switching, I would receive monthly security updates but haven't received one since switching to Xfinity. When I select "Check for Updates" it says "none available with last update from December 2022. I confirmed with Samsung that I should have mostly security updates and the latest Android 14 software update. Also, I was unable to get any information from Xfinity chat.

Can a Xfinity rep look into this? Thank you!