The text messages you are sending and receiving are they imessages (blue, iPhone)? That happened to me before, the SIM card had died, it was brand new. I activated an esim, and everything worked fine after that. Hope this helps!
Have you tried going to your settings? In your cellular settings, and under SIMs (might be different for Android, I have an iPhone). I had to enter my phone number there. Make sure that the sim that is “on” is the one from Public Mobile. You can also...
