Not receiving important group texts

I switched from ATT to Xfinity mobile about two weeks ago. I thought that the transition was seamless but then discovered that I was suddenly not receiving group texts from multiple threads. I completely missed two extremely important in person work meetings because of this. Everyone else in the group threads received all the messages-even the ones who use Verizon who carries my Xfinity mobile service. My iPhone is up to date. I’m starting to realize that “free for a year” isn’t worth [Edited: "Inappropriate Language"] if you’ll potentially lose your job over missed meetings. Hoping to find an easy fix for this before I go crawling back to ATT